# title: Count tokens in a Message url: https://platform.claude.com/docs/en/api/beta/messages/count_tokens

# Count tokens in a Message

POST /v1/messages/count_tokens

Count the number of tokens in a Message.

The Token Count API can be used to count the number of tokens in a Message, including tools, images, and documents, without creating it.

Learn more about token counting in our user guide

# Headers

• "anthropic-beta": optional array of AnthropicBeta

  Optional header to specify the beta version(s) you want to use.

  • string

  • "message-batches-2024-09-24" or "prompt-caching-2024-07-31" or "computer-use-2024-10-22" or 43 more

    • "message-batches-2024-09-24"

    • "prompt-caching-2024-07-31"

    • "computer-use-2024-10-22"

    • "computer-use-2025-01-24"

    • "pdfs-2024-09-25"

    • "token-counting-2024-11-01"

    • "token-efficient-tools-2025-02-19"

    • "output-128k-2025-02-19"

    • "files-api-2025-04-14"

    • "mcp-client-2025-04-04"

    • "mcp-client-2025-11-20"

    • "dev-full-thinking-2025-05-14"

    • "interleaved-thinking-2025-05-14"

    • "code-execution-2025-05-22"

    • "extended-cache-ttl-2025-04-11"

    • "context-1m-2025-08-07"

    • "context-management-2025-06-27"

    • "model-context-window-exceeded-2025-08-26"

    • "skills-2025-10-02"

    • "fast-mode-2026-02-01"

    • "output-300k-2026-03-24"

    • "user-profiles-2026-03-24"

    • "user-profiles-2026-08-18"

    • "user-profiles-2026-09-04"

    • "advisor-tool-2026-03-01"

    • "managed-agents-2026-04-01"

    • "cache-diagnosis-2026-04-07"

    • "dreaming-2026-04-21"

    • "thinking-token-count-2026-05-13"

    • "server-side-fallback-2026-06-01"

    • "server-side-fallback-2026-07-01"

    • "fallback-credit-2026-06-01"

    • "fallback-credit-2026-07-01"

    • "agent-memory-2026-07-22"

    • "mid-conversation-tool-changes-2026-07-01"

    • "compact-2026-01-12"

    • "computer-use-2025-11-24"

    • "mcp-tunnels-2026-06-22"

    • "structured-outputs-2025-11-13"

    • "task-budgets-2026-03-13"

    • "thinking-display-updates-2026-08-18"

    • "ce-user-management-2026-07-13"

    • "mid-conversation-output-config-2026-07-01"

    • "thinking-binding-controls-2026-08-01"

    • "mid-conversation-system-clear-at-2026-08-21"

    • "compact-2026-09-04"

• "anthropic-user-profile-id": optional string

  The user profile ID to attribute this request to. Use when acting on behalf of a party other than your organization. Requires the user-profiles beta header.

• "anthropic-workspace-id": optional string

# Body parameters

• messages: array of BetaMessageParam

  Input messages.

  Our models are trained to operate on alternating user and assistant conversational turns. When creating a new Message, you specify the prior conversational turns with the messages parameter, and the model then generates the next Message in the conversation. Consecutive user or assistant turns in your request will be combined into a single turn.

  Each input message must be an object with a role and content. You can specify a single user-role message, or you can include multiple user and assistant messages.

  If the final message uses the assistant role, the response content will continue immediately from the content in that message. This can be used to constrain part of the model's response.

  Example with a single user message:

  jsonCopy

  [{"role": "user", "content": "Hello, Claude"}]

  Example with multiple conversational turns:

  jsonCopy

  [
    {"role": "user", "content": "Hello there."},
    {"role": "assistant", "content": "Hi, I'm Claude. How can I help you?"},
    {"role": "user", "content": "Can you explain LLMs in plain English?"},
  ]

  Example with a partially-filled response from Claude:

  jsonCopy

  [
    {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
    {"role": "assistant", "content": "The best answer is ("},
  ]

  Each input message content may be either a single string or an array of content blocks, where each block has a specific type. Using a string for content is shorthand for an array of one content block of type "text". The following input messages are equivalent:

  jsonCopy

  {"role": "user", "content": "Hello, Claude"}

  jsonCopy

  {"role": "user", "content": [{"type": "text", "text": "Hello, Claude"}]}

  See input examples.

  Note that if you want to include a system prompt, you can use the top-level system parameter — there is no "system" role for input messages in the Messages API.

  There is a limit of 100,000 messages in a single request.

  • content: string or array of BetaContentBlockParam

    • string

    • array of BetaContentBlockParam

      • BetaTextBlockParam object

        • type: "text"

        • text: string

          minLength: 1

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

          • type: "ephemeral"

          • ttl: optional "5m" or "1h"

            The time-to-live for the cache control breakpoint.

            This may be one the following values:

            • 5m: 5 minutes
            • 1h: 1 hour

            Defaults to 5m. See prompt caching pricing for details.

            • "5m"

            • "1h"

        • citations: optional array of BetaTextCitationParam or null

          • BetaCitationCharLocationParam object

            • type: "char_location"

            • cited_text: string

            • document_index: number

              minimum: 0

            • document_title: string or null

              maxLength: 500, minLength: 1

            • end_char_index: number

            • start_char_index: number

              minimum: 0

          • BetaCitationPageLocationParam object

            • type: "page_location"

            • cited_text: string

            • document_index: number

              minimum: 0

            • document_title: string or null

              maxLength: 500, minLength: 1

            • end_page_number: number

            • start_page_number: number

              minimum: 1

          • BetaCitationContentBlockLocationParam object

            • type: "content_block_location"

            • cited_text: string

              The full text of the cited block range, concatenated.

              Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

            • document_index: number

              minimum: 0

            • document_title: string or null

              maxLength: 500, minLength: 1

            • end_block_index: number

              Exclusive 0-based end index of the cited block range in the source's content array.

              Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

            • start_block_index: number

              0-based index of the first cited block in the source's content array.

              minimum: 0

          • BetaCitationWebSearchResultLocationParam object

            • type: "web_search_result_location"

            • cited_text: string

            • encrypted_index: string

            • title: string or null

              maxLength: 512, minLength: 1

            • url: string

              minLength: 1

          • BetaCitationSearchResultLocationParam object

            • type: "search_result_location"

            • cited_text: string

              The full text of the cited block range, concatenated.

              Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

            • end_block_index: number

              Exclusive 0-based end index of the cited block range in the source's content array.

              Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

            • search_result_index: number

              0-based index of the cited search result among all search_result content blocks in the request, in the order they appear across messages and tool results.

              Counted separately from document_index; server-side web search results are not included in this count.

              minimum: 0

            • source: string

            • start_block_index: number

              0-based index of the first cited block in the source's content array.

              minimum: 0

            • title: string or null

      • BetaImageBlockParam object

        • type: "image"

        • source: BetaBase64ImageSource or BetaURLImageSource or BetaFileImageSource

          • BetaBase64ImageSource object

            • type: "base64"

            • data: string

              format: byte

            • media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"

              • "image/jpeg"

              • "image/png"

              • "image/gif"

              • "image/webp"

          • BetaURLImageSource object

            • type: "url"

            • url: string

          • BetaFileImageSource object

            • type: "file"

            • file_id: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • transformations: optional BetaImageTransformationsParam or null

          Configures the transformations the server applies to this image before the model observes it. Each key names a condition the server transforms images for; its value selects the transformation applied. Omitted keys keep their default behavior, and an empty object is equivalent to omitting the field.

          • oversized_image: optional "downsize" or "error"

            What the server does when this image exceeds the model's maximum image size. "downsize" (the default) scales the image down to fit, which changes the dimensions the model observes without telling you. "error" instead rejects the request with a 400 error naming the image's dimensions and the largest dimensions that fit, so you can scale the image deliberately — your image is never silently scaled down.

            • "downsize"

            • "error"

      • BetaRequestDocumentBlock object

        • type: "document"

        • source: BetaBase64PDFSource or BetaPlainTextSource or BetaContentBlockSource or 2 more

          • BetaBase64PDFSource object

            • type: "base64"

            • data: string

              format: byte

            • media_type: "application/pdf"

          • BetaPlainTextSource object

            • type: "text"

            • data: string

            • media_type: "text/plain"

          • BetaContentBlockSource object

            • type: "content"

            • content: string or array of BetaContentBlockSourceContent

              • string

              • BetaContentBlockSourceContent = array of BetaContentBlockSourceContent

                • BetaTextBlockParam object

                • BetaImageBlockParam object

          • BetaURLPDFSource object

            • type: "url"

            • url: string

          • BetaFileDocumentSource object

            • type: "file"

            • file_id: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • citations: optional BetaCitationsConfigParam or null

          • enabled: optional boolean

        • context: optional string or null

          minLength: 1

        • title: optional string or null

          maxLength: 500, minLength: 1

      • BetaSearchResultBlockParam object

        • type: "search_result"

        • content: array of BetaTextBlockParam

          • type: "text"

          • text: string

            minLength: 1

          • cache_control: optional BetaCacheControlEphemeral or null

            Create a cache control breakpoint at this content block.

          • citations: optional array of BetaTextCitationParam or null

        • source: string

        • title: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • citations: optional BetaCitationsConfigParam

      • BetaThinkingBlockParam object

        • type: "thinking"

        • signature: string

          The signature value of this thinking block, exactly as returned by the API in a previous response. Used to verify that the block was generated by Claude.

          Thinking blocks must be passed back unmodified and in their original order; a modified block results in a 400 invalid_request_error.

        • thinking: string

          The thinking text of this block as returned by the API.

      • BetaRedactedThinkingBlockParam object

        • type: "redacted_thinking"

        • data: string

          The data value of this redacted thinking block, exactly as returned by the API in a previous response. Opaque and encrypted; pass it back unchanged.

      • BetaToolUseBlockParam object

        • type: "tool_use"

        • id: string

          pattern: ^[1]+$

        • input: map[unknown]

        • name: string

          maxLength: 200, minLength: 1

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

            • type: "direct"

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

            • type: "code_execution_20250825"

            • tool_id: string

              pattern: ^srvtoolu_[a-zA-Z0-9_]+$

          • BetaServerToolCaller20260120 object

            • type: "code_execution_20260120"

            • tool_id: string

              pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • toolset_name: optional string or null

          For a toolset member tool_use, the toolset family this member belongs to.

          maxLength: 64, minLength: 1, pattern: ^[2]+$

      • BetaToolResultBlockParam object

        • type: "tool_result"

        • tool_use_id: string

          pattern: ^[3]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • content: optional string or array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 3 more

          • string

          • array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 3 more

            • BetaTextBlockParam object

            • BetaImageBlockParam object

            • BetaSearchResultBlockParam object

            • BetaRequestDocumentBlock object

            • BetaToolReferenceBlockParam object

              Tool reference block that can be included in tool_result content.

              • type: "tool_reference"

              • tool_name: string

                maxLength: 256, minLength: 1, pattern: ^[4]{1,256}$

              • cache_control: optional BetaCacheControlEphemeral or null

                Create a cache control breakpoint at this content block.

            • BetaBrowserStateBlockParam object

              The caller's browser state after a browser toolset member call — the full inventory of open tabs, which tab is active, and any side effects (tabs opened, download state changes) the call produced.

              At most one per tool_result, only on a non-error result answering a browser toolset member tool_use. The server renders the model-visible text from it; the model never sees the raw fields.

              • type: "browser_state"

              • tabs: array of BetaBrowserStateTabEntry

                All tabs open in the browser after this call — the full inventory, not a delta. May be empty. Whenever non-empty, exactly one entry carries active: true.

                maxItems: 100

                • tab_id: string

                  The caller-assigned identifier for this tab, unique within the inventory.

                  maxLength: 4096, minLength: 1, pattern: ^[5]*$

                • title: string

                  The title of the page the tab is showing. May be empty.

                  maxLength: 4096, pattern: ^[6]*$

                • url: string

                  The URL of the page the tab is showing. May be empty.

                  maxLength: 4096, pattern: ^[7]*$

                • active: optional boolean

                  Whether this tab is the active tab after this call. Whenever tabs is non-empty, exactly one entry is marked active: true.

              • cache_control: optional BetaCacheControlEphemeral or null

                Create a cache control breakpoint at this content block.

              • state_changes: optional array of BetaBrowserStateChange or null

                Tabs opened and download state changes during this call. "Nothing to report" is expressed by omitting the field, never by an empty list.

                maxItems: 200, minItems: 1

                • BetaBrowserStateChangeTabOpened object

                  A tab this call's execution opened that remains open at its end — the creation delta of the tabs inventory, not an event log.

                  Carries only the tab_id; the tab's title and url live on its tabs entry, which must include the same tab_id. A tab opened during a failed call gets no deferred tab_opened; it simply appears in the next result's tabs inventory.

                  • type: "tab_opened"

                  • tab_id: string

                    The tab_id of the opened tab, present in tabs.

                    maxLength: 4096, minLength: 1, pattern: ^[8]*$

                • BetaBrowserStateChangeDownloadStarted object

                  A file download that started during this call.

                  • type: "download_started"

                  • download_id: string

                    The caller-assigned identifier for this download, stable across the state changes reporting it.

                    maxLength: 4096, minLength: 1, pattern: ^[9]*$

                  • url: string

                    The final post-redirect URL the download was served from.

                    maxLength: 4096, pattern: ^[10]*$

                • BetaBrowserStateChangeDownloadCompleted object

                  A file download that finished during this call, reported with the same download_id as its download_started — or without a prior download_started, when the download finished during the call that started it (at most one state change per download_id per result).

                  • type: "download_completed"

                  • download_id: string

                    The caller-assigned identifier for this download, stable across the state changes reporting it.

                    maxLength: 4096, minLength: 1, pattern: ^[11]*$

                  • url: string

                    The final post-redirect URL the download was served from.

                    maxLength: 4096, pattern: ^[12]*$

                  • path: optional string or null

                    Where the executor saved the file, on the executor's filesystem. Only included when another tool in the same environment can read the file at that path.

                    pattern: ^[13]*$, maxLength: 4096

                  • size_bytes: optional number or null

                    The completed download's size.

                    minimum: 0

                • BetaBrowserStateChangeDownloadFailed object

                  A file download that failed — or was cancelled — during this call.

                  • type: "download_failed"

                  • download_id: string

                    The caller-assigned identifier for this download, stable across the state changes reporting it.

                    maxLength: 4096, minLength: 1, pattern: ^[14]*$

                  • url: string

                    The final post-redirect URL the download was served from.

                    maxLength: 4096, pattern: ^[15]*$

                  • error: optional string or null

                    The failure or cancellation detail, when known.

                    pattern: ^[16]*$, maxLength: 4096

        • is_error: optional boolean

        • toolset_name: optional string or null

          For a toolset member tool_result, the toolset family of the paired tool_use.

          maxLength: 64, minLength: 1, pattern: ^[17]+$

      • BetaServerToolUseBlockParam object

        • type: "server_tool_use"

        • id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • input: map[unknown]

        • name: "advisor" or "web_search" or "web_fetch" or 5 more

          • "advisor"

          • "web_search"

          • "web_fetch"

          • "code_execution"

          • "bash_code_execution"

          • "text_editor_code_execution"

          • "tool_search_tool_regex"

          • "tool_search_tool_bm25"

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object

      • BetaWebSearchToolResultBlockParam object

        • type: "web_search_tool_result"

        • content: BetaWebSearchToolResultBlockParamContent

          • ResultBlock = array of BetaWebSearchResultBlockParam

            • type: "web_search_result"

            • encrypted_content: string

            • title: string

            • url: string

            • page_age: optional string or null

          • BetaWebSearchToolRequestError object

            • type: "web_search_tool_result_error"

            • error_code: BetaWebSearchToolResultErrorCode

              • "invalid_tool_input"

              • "unavailable"

              • "max_uses_exceeded"

              • "too_many_requests"

              • "query_too_long"

              • "request_too_large"

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object

      • BetaWebFetchToolResultBlockParam object

        • type: "web_fetch_tool_result"

        • content: BetaWebFetchToolResultErrorBlockParam or BetaWebFetchBlockParam

          • BetaWebFetchToolResultErrorBlockParam object

            • type: "web_fetch_tool_result_error"

            • error_code: BetaWebFetchToolResultErrorCode

              • "invalid_tool_input"

              • "url_too_long"

              • "url_not_allowed"

              • "url_not_in_prior_context"

              • "url_not_accessible"

              • "unsupported_content_type"

              • "too_many_requests"

              • "max_uses_exceeded"

              • "unavailable"

              • "content_too_large"

          • BetaWebFetchBlockParam object

            • type: "web_fetch_result"

            • content: BetaRequestDocumentBlock

            • url: string

              Fetched content URL

            • retrieved_at: optional string or null

              ISO 8601 timestamp when the content was retrieved

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object

      • BetaAdvisorToolResultBlockParam object

        • type: "advisor_tool_result"

        • content: BetaAdvisorToolResultErrorParam or BetaAdvisorResultBlockParam or BetaAdvisorRedactedResultBlockParam

          • BetaAdvisorToolResultErrorParam object

            • type: "advisor_tool_result_error"

            • error_code: "max_uses_exceeded" or "prompt_too_long" or "too_many_requests" or 4 more

              • "max_uses_exceeded"

              • "prompt_too_long"

              • "too_many_requests"

              • "overloaded"

              • "unavailable"

              • "execution_time_exceeded"

              • "model_not_found"

          • BetaAdvisorResultBlockParam object

            • type: "advisor_result"

            • text: string

            • stop_reason: optional string or null

          • BetaAdvisorRedactedResultBlockParam object

            • type: "advisor_redacted_result"

            • encrypted_content: string

              Opaque blob produced by a prior response; must be round-tripped verbatim.

            • stop_reason: optional string or null

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaCodeExecutionToolResultBlockParam object

        • type: "code_execution_tool_result"

        • content: BetaCodeExecutionToolResultBlockParamContent

          • BetaCodeExecutionToolResultErrorParam object

            • type: "code_execution_tool_result_error"

            • error_code: BetaCodeExecutionToolResultErrorCode

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

          • BetaCodeExecutionResultBlockParam object

            • type: "code_execution_result"

            • content: array of BetaCodeExecutionOutputBlockParam

              • type: "code_execution_output"

              • file_id: string

            • return_code: number

            • stderr: string

            • stdout: string

          • BetaEncryptedCodeExecutionResultBlockParam object

            Code execution result with encrypted stdout for PFC + web_search results.

            • type: "encrypted_code_execution_result"

            • content: array of BetaCodeExecutionOutputBlockParam

              • type: "code_execution_output"

              • file_id: string

            • encrypted_stdout: string

            • return_code: number

            • stderr: string

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaBashCodeExecutionToolResultBlockParam object

        • type: "bash_code_execution_tool_result"

        • content: BetaBashCodeExecutionToolResultErrorParam or BetaBashCodeExecutionResultBlockParam

          • BetaBashCodeExecutionToolResultErrorParam object

            • type: "bash_code_execution_tool_result_error"

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

              • "output_file_too_large"

          • BetaBashCodeExecutionResultBlockParam object

            • type: "bash_code_execution_result"

            • content: array of BetaBashCodeExecutionOutputBlockParam

              • type: "bash_code_execution_output"

              • file_id: string

            • return_code: number

            • stderr: string

            • stdout: string

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaTextEditorCodeExecutionToolResultBlockParam object

        • type: "text_editor_code_execution_tool_result"

        • content: BetaTextEditorCodeExecutionToolResultErrorParam or BetaTextEditorCodeExecutionViewResultBlockParam or BetaTextEditorCodeExecutionCreateResultBlockParam or BetaTextEditorCodeExecutionStrReplaceResultBlockParam

          • BetaTextEditorCodeExecutionToolResultErrorParam object

            • type: "text_editor_code_execution_tool_result_error"

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

              • "file_not_found"

            • error_message: optional string or null

          • BetaTextEditorCodeExecutionViewResultBlockParam object

            • type: "text_editor_code_execution_view_result"

            • content: string

            • file_type: "text" or "image" or "pdf"

              • "text"

              • "image"

              • "pdf"

            • num_lines: optional number or null

            • start_line: optional number or null

            • total_lines: optional number or null

          • BetaTextEditorCodeExecutionCreateResultBlockParam object

            • type: "text_editor_code_execution_create_result"

            • is_file_update: boolean

          • BetaTextEditorCodeExecutionStrReplaceResultBlockParam object

            • type: "text_editor_code_execution_str_replace_result"

            • lines: optional array of string or null

            • new_lines: optional number or null

            • new_start: optional number or null

            • old_lines: optional number or null

            • old_start: optional number or null

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaToolSearchToolResultBlockParam object

        • type: "tool_search_tool_result"

        • content: BetaToolSearchToolResultErrorParam or BetaToolSearchToolSearchResultBlockParam

          • BetaToolSearchToolResultErrorParam object

            • type: "tool_search_tool_result_error"

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or "execution_time_exceeded"

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

            • error_message: optional string or null

          • BetaToolSearchToolSearchResultBlockParam object

            • type: "tool_search_tool_search_result"

            • tool_references: array of BetaToolReferenceBlockParam

              • type: "tool_reference"

              • tool_name: string

                maxLength: 256, minLength: 1, pattern: ^[18]{1,256}$

              • cache_control: optional BetaCacheControlEphemeral or null

                Create a cache control breakpoint at this content block.

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaMCPToolUseBlockParam object

        • type: "mcp_tool_use"

        • id: string

          pattern: ^[19]+$

        • input: map[unknown]

        • name: string

        • server_name: string

          The name of the MCP server

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaRequestMCPToolResultBlockParam object

        • type: "mcp_tool_result"

        • tool_use_id: string

          pattern: ^[20]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • content: optional string or array of BetaTextBlockParam

          • string

          • BetaMCPToolResultBlockParamContent = array of BetaTextBlockParam

            • type: "text"

            • text: string

              minLength: 1

            • cache_control: optional BetaCacheControlEphemeral or null

              Create a cache control breakpoint at this content block.

            • citations: optional array of BetaTextCitationParam or null

        • is_error: optional boolean

      • BetaContainerUploadBlockParam object

        A content block that represents a file to be uploaded to the container Files uploaded via this block will be available in the container's input directory.

        • type: "container_upload"

        • file_id: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaCompactionBlockParam object

        A compaction block containing summary of previous context.

        Users should round-trip these blocks from responses to subsequent requests to maintain context across compaction boundaries.

        When content is None, the block represents a failed compaction. The server treats these as no-ops. Empty string content is not allowed.

        • type: "compaction"

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • content: optional string or null

          Summary of previously compacted content, or null if compaction failed

        • encrypted_content: optional string or null

          Opaque metadata from prior compaction, to be round-tripped verbatim

        • signature: optional string or null

          The block's signature as returned, to be sent back verbatim

      • BetaRequestToolAdditionBlock object

        Mid-conversation directive to surface a declared tool.

        tool references a tool (or MCP toolset) by name from the request's tools; it is offered to the model from this point in the conversation onward.

        • type: "tool_addition"

        • tool: BetaToolChangeToolReference or BetaToolChangeMCPToolReference or BetaToolChangeMCPToolsetReference

          • BetaToolChangeToolReference object

            Reference to a single tool the caller declared directly in tools[]. Does not accept the composed {server}_{name} form the server assigns to MCP-resolved tools — use mcp_tool_reference or mcp_toolset_reference for those.

            • type: "tool_reference"

            • name: string

              pattern: ^[21]{1,128}$

          • BetaToolChangeMCPToolReference object

            Reference to a single MCP tool by its server and remote name; the same server_name/name pair mcp_tool_use carries.

            • type: "mcp_tool_reference"

            • name: string

            • server_name: string

          • BetaToolChangeMCPToolsetReference object

            Reference to every tool in the named MCP server's toolset.

            • type: "mcp_toolset_reference"

            • server_name: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaRequestToolRemovalBlock object

        Mid-conversation directive to withdraw a tool.

        tool references a tool (or MCP toolset) by name from the request's tools; it is no longer offered to the model from this point in the conversation onward.

        • type: "tool_removal"

        • tool: BetaToolChangeToolReference or BetaToolChangeMCPToolReference or BetaToolChangeMCPToolsetReference

          • BetaToolChangeToolReference object

            Reference to a single tool the caller declared directly in tools[]. Does not accept the composed {server}_{name} form the server assigns to MCP-resolved tools — use mcp_tool_reference or mcp_toolset_reference for those.

          • BetaToolChangeMCPToolReference object

            Reference to a single MCP tool by its server and remote name; the same server_name/name pair mcp_tool_use carries.

          • BetaToolChangeMCPToolsetReference object

            Reference to every tool in the named MCP server's toolset.

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaFallbackBlockParam object

        A fallback block echoed back from a prior response.

        Accepted in messages[].content and not rendered into the prompt; not validated against the request's fallbacks chain or top-level model.

        Echo the assistant turn back verbatim, including this block in its original position. The block marks the boundary between content produced before and after a fallback hop, and the server relies on that boundary to validate the turn: when thinking runs flank the boundary, omitting the block merges them into one span the server cannot validate (the request is rejected), and moving it into the middle of a single run is likewise rejected; between non-thinking blocks the block's placement has no validation effect.

        • type: "fallback"

        • from: BetaFallbackInfoParam

          Identifies one hop of a fallback transition.

          • model: Model

            The model that will complete your prompt.

            See models for additional details and options.

            • "claude-fable-5-1" or "claude-mythos-5-1" or "claude-sonnet-5" or 14 more

              The model that will complete your prompt.

              See models for additional details and options.

              • "claude-fable-5-1"

                Frontier intelligence for ambitious tasks across coding, scientific discovery, and enterprise workflows

              • "claude-mythos-5-1"

                Our most capable model for cybersecurity and biology research, available through trusted access programs

              • "claude-sonnet-5"

                High-performance model for coding and agents

              • "claude-fable-5"

                Next generation of intelligence for the hardest knowledge work and coding problems

              • "claude-mythos-5"

                Most capable model for cybersecurity and biology research

              • "claude-opus-5"

                Powerful intelligence for long-running agents and coding

              • "claude-opus-4-8"

                Powerful intelligence for long-running agents and coding

              • "claude-opus-4-7"

                Powerful intelligence for long-running agents and coding

              • "claude-mythos-preview"

                New class of intelligence, strongest in coding and cybersecurity

              • "claude-opus-4-6"

                Powerful intelligence for long-running agents and coding

              • "claude-sonnet-4-6"

                Best combination of speed and intelligence

              • "claude-haiku-4-5"

                Fastest model with near-frontier intelligence

              • "claude-haiku-4-5-20251001"

                Fastest model with near-frontier intelligence

              • "claude-opus-4-5"

                Powerful intelligence for long-running agents and coding

              • "claude-opus-4-5-20251101"

                Powerful intelligence for long-running agents and coding

              • "claude-sonnet-4-5"

                High-performance model for agents and coding

              • "claude-sonnet-4-5-20250929"

                High-performance model for agents and coding

            • string

        • to: BetaFallbackInfoParam

          Identifies one hop of a fallback transition.

        • trigger: optional unknown

          The response block's trigger, echoed verbatim. Accepted and ignored by the server; any object or null is allowed.

  • role: "user" or "assistant" or "system"

    • "user"

    • "assistant"

    • "system"

  • clear_at: optional "next_user_message" or "never" or null

    How long this system message's text stays in front of the model. "never" (the default) renders it on every request that includes it. "next_user_message" renders it only for the user turn it follows: once a later role: "user" message exists in messages the message stays in the array (send it unchanged) but is no longer shown to the model. Only permitted on role: "system" messages.

    • "next_user_message"

    • "never"

  • output_config: optional BetaSystemMessageOutputConfig or null

    Per-message output configuration on a role:"system" input message.

    Fields here apply per-turn; format remains top-level only. An empty {} is accepted on a message that carries content; a message with neither content nor output_config fields is rejected.

    • effort: optional "low" or "medium" or "high" or 2 more or null

      All possible effort levels.

      • "low"

      • "medium"

      • "high"

      • "xhigh"

      • "max"

• model: Model

  The model that will complete your prompt.

  See models for additional details and options.

• cache_control: optional BetaCacheControlEphemeral or null

  Top-level cache control automatically applies a cache_control marker to the last cacheable block in the request.

• compaction: optional BetaCompactionConfig or null

  Compact the whole conversation and return a signed compaction block, alone, that a later request sends back first in messages, in place of the messages it summarizes. There is no trigger and no pause flag: sending the parameter compacts, and nothing is sampled after the block.

  The summarization prompt is the server's own unless instructions are given, which then replace it for this request; a value that is empty or only whitespace counts as absent.

  • type: "summarize"

  • instructions: optional string or null

    Replaces the server's default summarization prompt for this request. An empty or whitespace-only value counts as absent.

    maxLength: 16384

• context_management: optional BetaContextManagementConfig or null

  Context management configuration.

  This allows you to control how Claude manages context across multiple requests, such as whether to clear function results or not.

  • edits: optional array of BetaClearToolUses20250919Edit or BetaClearThinking20251015Edit or BetaCompact20260112Edit

    List of context management edits to apply

    minItems: 0

    • BetaClearToolUses20250919Edit object

      • type: "clear_tool_uses_20250919"

      • clear_at_least: optional BetaInputTokensClearAtLeast or null

        Minimum number of tokens that must be cleared when triggered. Context will only be modified if at least this many tokens can be removed.

        • type: "input_tokens"

        • value: number

          minimum: 0

      • clear_tool_inputs: optional boolean or array of string or null

        Whether to clear all tool inputs (bool) or specific tool inputs to clear (list)

        • boolean

        • array of string

      • exclude_tools: optional array of string or null

        Tool names whose uses are preserved from clearing

      • keep: optional BetaToolUsesKeep

        Number of tool uses to retain in the conversation

        • type: "tool_uses"

        • value: number

          minimum: 0

      • trigger: optional BetaInputTokensTrigger or BetaToolUsesTrigger

        Condition that triggers the context management strategy

        • BetaInputTokensTrigger object

          • type: "input_tokens"

          • value: number

            minimum: 1

        • BetaToolUsesTrigger object

          • type: "tool_uses"

          • value: number

            minimum: 1

    • BetaClearThinking20251015Edit object

      • type: "clear_thinking_20251015"

      • keep: optional BetaThinkingTurns or BetaAllThinkingTurns or "all"

        Number of most recent assistant turns to keep thinking blocks for. Older turns will have their thinking blocks removed.

        • BetaThinkingTurns object

          • type: "thinking_turns"

          • value: number

            minimum: 1

        • BetaAllThinkingTurns object

          • type: "all"

        • "all"

    • BetaCompact20260112Edit object

      Automatically compact older context when reaching the configured trigger threshold.

      • type: "compact_20260112"

      • instructions: optional string or null

        Additional instructions for summarization.

      • pause_after_compaction: optional boolean

        Whether to pause after compaction and return the compaction block to the user.

      • trigger: optional BetaInputTokensTrigger or null

        When to trigger compaction. Defaults to 150000 input tokens.

• mcp_servers: optional array of BetaRequestMCPServerURLDefinition

  MCP servers to be utilized in this request

  maxItems: 20

  • type: "url"

  • name: string

  • url: string

  • authorization_token: optional string or null

  • tool_configuration: optional BetaRequestMCPServerToolConfiguration or null

    • allowed_tools: optional array of string or null

    • enabled: optional boolean or null

• output_config: optional BetaOutputConfig

  Configuration options for the model's output, such as the output format.

  • effort: optional "low" or "medium" or "high" or 2 more or null

    All possible effort levels.

    • "low"

    • "medium"

    • "high"

    • "xhigh"

    • "max"

  • format: optional BetaJSONOutputFormat or null

    A schema to specify Claude's output format in responses. See structured outputs

    • type: "json_schema"

    • schema: map[unknown]

      The JSON schema of the format

  • task_budget: optional BetaTokenTaskBudget or null

    User-configurable total token budget across contexts.

    • type: "tokens"

      The budget type. Currently only 'tokens' is supported.

    • total: number

      Total token budget across all contexts in the session.

      minimum: 1024

    • remaining: optional number or null

      Remaining tokens in the budget. Use this to track usage across contexts when implementing compaction client-side. Defaults to total if not provided.

      minimum: 0

• speed: optional "standard" or "fast" or null

  Inference speed mode. fast provides significantly faster output token generation at premium pricing. Not all models support fast; invalid combinations are rejected at create time.

  • "standard"

  • "fast"

• system: optional string or array of BetaTextBlockParam

  System prompt.

  A system prompt is a way of providing context and instructions to Claude, such as specifying a particular goal or role. See our guide to system prompts.

  • string

  • array of BetaTextBlockParam

    • type: "text"

    • text: string

      minLength: 1

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional array of BetaTextCitationParam or null

• thinking: optional BetaThinkingConfigParam

  Configuration for enabling Claude's extended thinking.

  When enabled, responses include thinking content blocks showing Claude's thinking process before the final answer. Requires a minimum budget of 1,024 tokens and counts towards your max_tokens limit.

  See extended thinking for details.

  • BetaThinkingConfigEnabled object

    • type: "enabled"

    • budget_tokens: number

      Determines how many tokens Claude can use for its internal reasoning process. Larger budgets can enable more thorough analysis for complex problems, improving response quality.

      Must be ≥1024 and less than max_tokens.

      See extended thinking for details.

      minimum: 1024

    • block_binding: optional BetaThinkingBlockBinding or null

      Controls for block binding: what happens when a thinking block this request sends back fails the conversation check. Every field is optional; an empty object means every default.

      • prefix_mismatch_behavior: optional BetaThinkingPrefixMismatchBehavior or null

        What happens when a thinking block in messages fails the conversation check: it was created in a different conversation, or the messages before it have changed since. "error" (the default) fails the request with a 400 error. "drop_block" removes the failing blocks and the request proceeds; the model no longer sees the dropped reasoning.

        • "error"

        • "drop_block"

    • display: optional "summarized" or "omitted" or "updates" or null

      Controls how thinking content appears in the response. When set to summarized, thinking is returned normally. When set to omitted, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to summarized.

      • "summarized"

      • "omitted"

      • "updates"

  • BetaThinkingConfigDisabled object

    • type: "disabled"

  • BetaThinkingConfigAdaptive object

    • type: "adaptive"

    • block_binding: optional BetaThinkingBlockBinding or null

      Controls for block binding: what happens when a thinking block this request sends back fails the conversation check. Every field is optional; an empty object means every default.

    • display: optional "summarized" or "omitted" or "updates" or null

      Controls how thinking content appears in the response. When set to summarized, thinking is returned normally. When set to omitted, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to summarized.

      • "summarized"

      • "omitted"

      • "updates"

• tool_choice: optional BetaToolChoice

  How the model should use the provided tools. The model can use a specific tool, any available tool, decide by itself, or not use tools at all.

  • BetaToolChoiceAuto object

    The model will automatically decide whether to use tools.

    • type: "auto"

    • disable_parallel_tool_use: optional boolean

      Whether to disable parallel tool use.

      Defaults to false. If set to true, the model will output at most one tool use.

  • BetaToolChoiceAny object

    The model will use any available tools.

    • type: "any"

    • disable_parallel_tool_use: optional boolean

      Whether to disable parallel tool use.

      Defaults to false. If set to true, the model will output exactly one tool use.

  • BetaToolChoiceTool object

    The model will use the specified tool with tool_choice.name.

    • type: "tool"

    • name: string

      The name of the tool to use.

    • disable_parallel_tool_use: optional boolean

      Whether to disable parallel tool use.

      Defaults to false. If set to true, the model will output exactly one tool use.

  • BetaToolChoiceNone object

    The model will not be allowed to use tools.

    • type: "none"

• tools: optional array of BetaTool or BetaToolBash20241022 or BetaToolBash20250124 or 25 more

  Definitions of tools that the model may use.

  If you include tools in your API request, the model may return tool_use content blocks that represent the model's use of those tools. You can then run those tools using the tool input generated by the model and then optionally return results back to the model using tool_result content blocks.

  There are two types of tools: client tools and server tools. The behavior described below applies to client tools. For server tools, see their individual documentation as each has its own behavior (e.g., the web search tool).

  Each tool definition includes:

  • name: Name of the tool.
  • description: Optional, but strongly-recommended description of the tool.
  • input_schema: JSON schema for the tool input shape that the model will produce in tool_use output content blocks.

  For example, if you defined tools as:

  jsonCopy

  [
    {
      "name": "get_stock_price",
      "description": "Get the current stock price for a given ticker symbol.",
      "input_schema": {
        "type": "object",
        "properties": {
          "ticker": {
            "type": "string",
            "description": "The stock ticker symbol, e.g. AAPL for Apple Inc."
          }
        },
        "required": ["ticker"]
      }
    }
  ]

  And then asked the model "What's the S&P 500 at today?", the model might produce tool_use content blocks in the response like this:

  jsonCopy

  [
    {
      "type": "tool_use",
      "id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
      "name": "get_stock_price",
      "input": { "ticker": "^GSPC" }
    }
  ]

  You might then run your get_stock_price tool with {"ticker": "^GSPC"} as an input, and return the following back to the model in a subsequent user message:

  jsonCopy

  [
    {
      "type": "tool_result",
      "tool_use_id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
      "content": "259.75 USD"
    }
  ]

  Tools can be used for workflows that include running client-side tools and functions, or more generally whenever you want the model to produce a particular JSON structure of output.

  See our guide for more details.

  • BetaTool object

    • type: optional "custom" or null

    • input_schema: object

      JSON schema for this tool's input.

      This defines the shape of the input that your tool accepts and that the model will produce.

      • type: "object"

      • properties: optional map[unknown] or null

      • required: optional array of string or null

    • name: string

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

      maxLength: 128, minLength: 1, pattern: ^[22]{1,128}$

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • description: optional string

      Description of what this tool does.

      Tool descriptions should be as detailed as possible. The more information that the model has about what the tool is and how to use it, the better it will perform. You can use natural language descriptions to reinforce important aspects of the tool input JSON schema.

    • eager_input_streaming: optional boolean or null

      Enable eager input streaming for this tool. When true, tool input parameters will be streamed incrementally as they are generated, and types will be inferred on-the-fly rather than buffering the full JSON output. When false, streaming is disabled for this tool even if the fine-grained-tool-streaming beta is active. When null (default), uses the default behavior based on beta headers.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolBash20241022 object

    • type: "bash_20241022"

    • name: "bash"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolBash20250124 object

    • type: "bash_20250124"

    • name: "bash"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20250522 object

    • type: "code_execution_20250522"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20250825 object

    • type: "code_execution_20250825"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20260120 object

    Code execution tool with REPL state persistence (daemon mode + gVisor checkpoint).

    • type: "code_execution_20260120"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20260521 object

    Code execution tool with REPL state persistence.

    • type: "code_execution_20260521"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaBrowserToolset20260801 object

    The browser toolset: a single tools[] entry (carrying no name) that declares the browser tool family. The model is served the family's tool with any members disabled via configs removed from its schema.

    • type: "browser_toolset_20260801"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • configs: optional BetaBrowserToolsetConfigs or null

      Per-member configuration for browser_toolset_20260801: one optional field per member tool, keyed by the member name — the same name the member's tool_use blocks carry. Every member is an accepted key, and a member's defaults apply wherever its key is absent. Unknown keys are rejected: the field set is this toolset version's complete member set.

      • type: optional BetaBrowserTypeConfig or null

        type's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • close_tab: optional BetaBrowserCloseTabConfig or null

        close_tab's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • double_click: optional BetaBrowserDoubleClickConfig or null

        double_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • file_upload: optional BetaBrowserFileUploadConfig or null

        file_upload's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • find: optional BetaBrowserFindConfig or null

        find's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • form_input: optional BetaBrowserFormInputConfig or null

        form_input's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • get_page_text: optional BetaBrowserGetPageTextConfig or null

        get_page_text's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • hold_key: optional BetaBrowserHoldKeyConfig or null

        hold_key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • hover: optional BetaBrowserHoverConfig or null

        hover's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • javascript_exec: optional BetaBrowserJavascriptExecConfig or null

        javascript_exec's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • key: optional BetaBrowserKeyConfig or null

        key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click: optional BetaBrowserLeftClickConfig or null

        left_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click_drag: optional BetaBrowserLeftClickDragConfig or null

        left_click_drag's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_down: optional BetaBrowserLeftMouseDownConfig or null

        left_mouse_down's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_up: optional BetaBrowserLeftMouseUpConfig or null

        left_mouse_up's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • list_tabs: optional BetaBrowserListTabsConfig or null

        list_tabs's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • middle_click: optional BetaBrowserMiddleClickConfig or null

        middle_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • mouse_move: optional BetaBrowserMouseMoveConfig or null

        mouse_move's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • navigate: optional BetaBrowserNavigateConfig or null

        navigate's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • new_tab: optional BetaBrowserNewTabConfig or null

        new_tab's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • read_console: optional BetaBrowserReadConsoleConfig or null

        read_console's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • read_network: optional BetaBrowserReadNetworkConfig or null

        read_network's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • read_page: optional BetaBrowserReadPageConfig or null

        read_page's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • right_click: optional BetaBrowserRightClickConfig or null

        right_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • screenshot: optional BetaBrowserScreenshotConfig or null

        screenshot's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • scroll: optional BetaBrowserScrollConfig or null

        scroll's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • scroll_to: optional BetaBrowserScrollToConfig or null

        scroll_to's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • switch_tab: optional BetaBrowserSwitchTabConfig or null

        switch_tab's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • triple_click: optional BetaBrowserTripleClickConfig or null

        triple_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • wait: optional BetaBrowserWaitConfig or null

        wait's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • zoom: optional BetaBrowserZoomConfig or null

        zoom's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

  • BetaToolComputerUse20241022 object

    • type: "computer_20241022"

    • display_height_px: number

      The height of the display in pixels.

      minimum: 1

    • display_width_px: number

      The width of the display in pixels.

      minimum: 1

    • name: "computer"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • display_number: optional number or null

      The X11 display number (e.g. 0, 1) for the display.

      minimum: 0

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaMemoryTool20250818 object

    • type: "memory_20250818"

    • name: "memory"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolComputerUse20250124 object

    • type: "computer_20250124"

    • display_height_px: number

      The height of the display in pixels.

      minimum: 1

    • display_width_px: number

      The width of the display in pixels.

      minimum: 1

    • name: "computer"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • display_number: optional number or null

      The X11 display number (e.g. 0, 1) for the display.

      minimum: 0

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20241022 object

    • type: "text_editor_20241022"

    • name: "str_replace_editor"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolComputerUse20251124 object

    • type: "computer_20251124"

    • display_height_px: number

      The height of the display in pixels.

      minimum: 1

    • display_width_px: number

      The width of the display in pixels.

      minimum: 1

    • name: "computer"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • display_number: optional number or null

      The X11 display number (e.g. 0, 1) for the display.

      minimum: 0

    • enable_zoom: optional boolean

      Whether to enable an action to take a zoomed-in screenshot of the screen.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaComputerToolset20260801 object

    The computer toolset: a single tools[] entry (carrying no name) that declares the computer tool family. The model is served the family's tool with any members disabled via configs removed from its schema. Every member is enabled by default, zoom included. The single-tool options display_number and enable_zoom are not fields of a toolset entry — it carries only type, configs, and cache_control; zoom is controlled via configs.zoom.enabled.

    • type: "computer_toolset_20260801"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • configs: optional BetaComputerToolsetConfigs or null

      Per-member configuration for computer_toolset_20260801: one optional field per member tool, keyed by the member name — the same name the member's tool_use blocks carry. Every member is an accepted key, and a member's defaults apply wherever its key is absent. Unknown keys are rejected: the field set is this toolset version's complete member set.

      • type: optional BetaComputerTypeConfig or null

        type's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • cursor_position: optional BetaComputerCursorPositionConfig or null

        cursor_position's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • double_click: optional BetaComputerDoubleClickConfig or null

        double_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • hold_key: optional BetaComputerHoldKeyConfig or null

        hold_key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • key: optional BetaComputerKeyConfig or null

        key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click: optional BetaComputerLeftClickConfig or null

        left_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click_drag: optional BetaComputerLeftClickDragConfig or null

        left_click_drag's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_down: optional BetaComputerLeftMouseDownConfig or null

        left_mouse_down's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_up: optional BetaComputerLeftMouseUpConfig or null

        left_mouse_up's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • middle_click: optional BetaComputerMiddleClickConfig or null

        middle_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • mouse_move: optional BetaComputerMouseMoveConfig or null

        mouse_move's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • right_click: optional BetaComputerRightClickConfig or null

        right_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • screenshot: optional BetaComputerScreenshotConfig or null

        screenshot's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • scroll: optional BetaComputerScrollConfig or null

        scroll's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • triple_click: optional BetaComputerTripleClickConfig or null

        triple_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • wait: optional BetaComputerWaitConfig or null

        wait's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • zoom: optional BetaComputerZoomConfig or null

        zoom's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

  • BetaToolTextEditor20250124 object

    • type: "text_editor_20250124"

    • name: "str_replace_editor"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20250429 object

    • type: "text_editor_20250429"

    • name: "str_replace_based_edit_tool"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20250728 object

    • type: "text_editor_20250728"

    • name: "str_replace_based_edit_tool"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • max_characters: optional number or null

      Maximum number of characters to display when viewing a file. If not specified, defaults to displaying the full file.

      minimum: 1

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaWebSearchTool20250305 object

    • type: "web_search_20250305"

    • name: "web_search"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

    • blocked_domains: optional array of string or null

      If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • user_location: optional BetaUserLocation or null

      Parameters for the user's location. Used to provide more relevant search results.

      • type: "approximate"

      • city: optional string or null

        The city of the user.

        maxLength: 255, minLength: 1

      • country: optional string or null

        The two letter ISO country code of the user.

        maxLength: 2, minLength: 2

      • region: optional string or null

        The region of the user.

        maxLength: 255, minLength: 1

      • timezone: optional string or null

        The IANA timezone of the user.

        maxLength: 255, minLength: 1

  • BetaWebFetchTool20250910 object

    • type: "web_fetch_20250910"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

      • client_tool_results: optional BetaWebFetchURLSourceAll or BetaWebFetchURLSourceNone or BetaWebFetchURLSourceOnly or BetaWebFetchURLSourceExcept

        Which client tools' results contribute fetchable URLs: "all", "none", or an only or except list of client tool names from tools[].

        • BetaWebFetchURLSourceAll object

          The url_sources variant under which a source contributes in full: every result of the tool filter's source, or all user input.

          • type: "all"

        • BetaWebFetchURLSourceNone object

          The url_sources variant under which a source contributes nothing: no result of the tool filter's source, or no user input.

          • type: "none"

        • BetaWebFetchURLSourceOnly object

          The tool filter variant under which only the named tools' results contribute.

          • type: "only"

          • tools: array of BetaWebFetchURLSourceToolReference

            • type: "tool_reference"

            • name: string

        • BetaWebFetchURLSourceExcept object

          The tool filter variant under which every result but the named tools' contributes.

          • type: "except"

          • tools: array of BetaWebFetchURLSourceToolReference

            • type: "tool_reference"

            • name: string

      • server_tool_results: optional BetaWebFetchURLSourceAll or BetaWebFetchURLSourceNone or BetaWebFetchURLSourceOnly or BetaWebFetchURLSourceExcept

        Which server tools' results contribute fetchable URLs: "all", "none", or an only or except list of server tool names from tools[]; only web_search and web_fetch results ever contribute.

        • BetaWebFetchURLSourceAll object

          The url_sources variant under which a source contributes in full: every result of the tool filter's source, or all user input.

        • BetaWebFetchURLSourceNone object

          The url_sources variant under which a source contributes nothing: no result of the tool filter's source, or no user input.

        • BetaWebFetchURLSourceOnly object

          The tool filter variant under which only the named tools' results contribute.

        • BetaWebFetchURLSourceExcept object

          The tool filter variant under which every result but the named tools' contributes.

      • user_input: optional BetaWebFetchURLSourceAll or BetaWebFetchURLSourceNone

        Whether URLs in user messages are fetchable: "all" or "none".

        • BetaWebFetchURLSourceAll object

          The url_sources variant under which a source contributes in full: every result of the tool filter's source, or all user input.

        • BetaWebFetchURLSourceNone object

          The url_sources variant under which a source contributes nothing: no result of the tool filter's source, or no user input.

  • BetaWebSearchTool20260209 object

    • type: "web_search_20260209"

    • name: "web_search"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

    • blocked_domains: optional array of string or null

      If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • user_location: optional BetaUserLocation or null

      Parameters for the user's location. Used to provide more relevant search results.

  • BetaWebFetchTool20260209 object

    • type: "web_fetch_20260209"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

  • BetaWebFetchTool20260309 object

    Web fetch tool with use_cache parameter for bypassing cached content.

    • type: "web_fetch_20260309"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

    • use_cache: optional boolean

      Whether to use cached content. Set to false to bypass the cache and fetch fresh content. Only set to false when the user explicitly requests fresh content or when fetching rapidly-changing sources.

  • BetaWebSearchTool20260318 object

    • type: "web_search_20260318"

    • name: "web_search"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

    • blocked_domains: optional array of string or null

      If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • response_inclusion: optional "full" or "excluded"

      How this tool's result blocks appear in the API response when the result was consumed by a completed code_execution call in the same turn. 'full' returns the complete content (default). 'excluded' drops the nested server_tool_use and result block pair entirely. Results from direct calls, or from code_execution calls that paused before completing, are always returned in full so they can be sent back on the next turn.

      • "full"

      • "excluded"

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • user_location: optional BetaUserLocation or null

      Parameters for the user's location. Used to provide more relevant search results.

  • BetaWebFetchTool20260318 object

    • type: "web_fetch_20260318"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • response_inclusion: optional "full" or "excluded"

      How this tool's result blocks appear in the API response when the result was consumed by a completed code_execution call in the same turn. 'full' returns the complete content (default). 'excluded' drops the nested server_tool_use and result block pair entirely. Results from direct calls, or from code_execution calls that paused before completing, are always returned in full so they can be sent back on the next turn.

      • "full"

      • "excluded"

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

    • use_cache: optional boolean

      Whether to use cached content. Set to false to bypass the cache and fetch fresh content. Only set to false when the user explicitly requests fresh content or when fetching rapidly-changing sources.

  • BetaAdvisorTool20260301 object

    • type: "advisor_20260301"

    • model: Model

      The model that will complete your prompt.

      See models for additional details and options.

    • name: "advisor"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • caching: optional BetaCacheControlEphemeral or null

      Caching for the advisor's own prompt. When set, each advisor call writes a cache entry at the given TTL so subsequent calls in the same conversation read the stable prefix. When omitted, the advisor prompt is not cached.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_tokens: optional number or null

      Bounds the advisor's total output (thinking + text) per call. When the advisor hits this cap, the returned advisor_result or advisor_redacted_result block carries stop_reason='max_tokens', and a truncation note is appended to the advice text the worker model sees (inside the encrypted blob in redacted mode). When set, the server also emits a remaining-tokens budget block in the advisor's prompt so the advisor self-shapes toward the cap. When omitted, the advisor model's default output cap applies and no budget block is emitted.

      minimum: 1024

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolSearchToolBm25_20251119 object

    • type: "tool_search_tool_bm25_20251119" or "tool_search_tool_bm25"

      • "tool_search_tool_bm25_20251119"

      • "tool_search_tool_bm25"

    • name: "tool_search_tool_bm25"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolSearchToolRegex20251119 object

    • type: "tool_search_tool_regex_20251119" or "tool_search_tool_regex"

      • "tool_search_tool_regex_20251119"

      • "tool_search_tool_regex"

    • name: "tool_search_tool_regex"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaMCPToolset object

    Configuration for a group of tools from an MCP server.

    Allows configuring enabled status and defer_loading for all tools from an MCP server, with optional per-tool overrides.

    • type: "mcp_toolset"

    • mcp_server_name: string

      Name of the MCP server to configure tools for

      maxLength: 255, minLength: 1

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • configs: optional map[BetaMCPToolConfig] or null

      Configuration overrides for specific tools, keyed by tool name

      • defer_loading: optional boolean

      • enabled: optional boolean

    • default_config: optional BetaMCPToolDefaultConfig

      Default configuration applied to all tools from this server

      • defer_loading: optional boolean

      • enabled: optional boolean

• output_format: optional BetaJSONOutputFormat or null

  Deprecated

  Deprecated: Use output_config.format instead. See structured outputs

  A schema to specify Claude's output format in responses. This parameter will be removed in a future release.

# Returns

• BetaMessageTokensCount object

  • context_management: BetaCountTokensContextManagementResponse or null

    Information about context management applied to the message.

    • original_input_tokens: number

      The original token count before context management was applied

  • input_tokens: number

    The total number of tokens across the provided list of messages, system prompt, and tools.

# Example

curl https://api.anthropic.com/v1/messages/count_tokens \
    -H 'Content-Type: application/json' \
    -H 'anthropic-version: 2023-06-01' \
    -H "X-Api-Key: $ANTHROPIC_API_KEY" \
    -d '{
          "messages": [
            {
              "content": "Hello, world",
              "role": "user"
            }
          ],
          "model": "claude-opus-5",
          "system": [
            {
              "text": "Today'\''s date is 2024-06-01.",
              "type": "text"
            }
          ],
          "thinking": {
            "type": "adaptive"
          },
          "tools": [
            {
              "input_schema": {
                "type": "object",
                "properties": {
                  "location": "bar",
                  "unit": "bar"
                },
                "required": [
                  "location"
                ]
              },
              "name": "name"
            }
          ]
        }'

# Response (200)

{
  "context_management": {
    "original_input_tokens": 0
  },
  "input_tokens": 2095
}