## 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](https://docs.claude.com/en/docs/build-with-claude/token-counting)

### Header Parameters

- `"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 23 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"`

    - `"advisor-tool-2026-03-01"`

    - `"managed-agents-2026-04-01"`

    - `"cache-diagnosis-2026-04-07"`

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

### 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:

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

  Example with multiple conversational turns:

  ```json
  [
    {"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:

  ```json
  [
    {"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:

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

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

  See [input examples](https://docs.claude.com/en/api/messages-examples).

  Note that if you want to include a [system prompt](https://docs.claude.com/en/docs/system-prompts), 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 { text, type, cache_control, citations }`

        - `text: string`

        - `type: "text"`

          - `"text"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

          - `type: "ephemeral"`

            - `"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`.

            - `"5m"`

            - `"1h"`

        - `citations: optional array of BetaTextCitationParam`

          - `BetaCitationCharLocationParam object { cited_text, document_index, document_title, 3 more }`

            - `cited_text: string`

            - `document_index: number`

            - `document_title: string`

            - `end_char_index: number`

            - `start_char_index: number`

            - `type: "char_location"`

              - `"char_location"`

          - `BetaCitationPageLocationParam object { cited_text, document_index, document_title, 3 more }`

            - `cited_text: string`

            - `document_index: number`

            - `document_title: string`

            - `end_page_number: number`

            - `start_page_number: number`

            - `type: "page_location"`

              - `"page_location"`

          - `BetaCitationContentBlockLocationParam object { cited_text, document_index, document_title, 3 more }`

            - `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`

            - `document_title: string`

            - `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.

            - `type: "content_block_location"`

              - `"content_block_location"`

          - `BetaCitationWebSearchResultLocationParam object { cited_text, encrypted_index, title, 2 more }`

            - `cited_text: string`

            - `encrypted_index: string`

            - `title: string`

            - `type: "web_search_result_location"`

              - `"web_search_result_location"`

            - `url: string`

          - `BetaCitationSearchResultLocationParam object { cited_text, end_block_index, search_result_index, 4 more }`

            - `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.

            - `source: string`

            - `start_block_index: number`

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

            - `title: string`

            - `type: "search_result_location"`

              - `"search_result_location"`

      - `BetaImageBlockParam object { source, type, cache_control }`

        - `source: BetaBase64ImageSource or BetaURLImageSource or BetaFileImageSource`

          - `BetaBase64ImageSource object { data, media_type, type }`

            - `data: string`

            - `media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"`

              - `"image/jpeg"`

              - `"image/png"`

              - `"image/gif"`

              - `"image/webp"`

            - `type: "base64"`

              - `"base64"`

          - `BetaURLImageSource object { type, url }`

            - `type: "url"`

              - `"url"`

            - `url: string`

          - `BetaFileImageSource object { file_id, type }`

            - `file_id: string`

            - `type: "file"`

              - `"file"`

        - `type: "image"`

          - `"image"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaRequestDocumentBlock object { source, type, cache_control, 3 more }`

        - `source: BetaBase64PDFSource or BetaPlainTextSource or BetaContentBlockSource or 2 more`

          - `BetaBase64PDFSource object { data, media_type, type }`

            - `data: string`

            - `media_type: "application/pdf"`

              - `"application/pdf"`

            - `type: "base64"`

              - `"base64"`

          - `BetaPlainTextSource object { data, media_type, type }`

            - `data: string`

            - `media_type: "text/plain"`

              - `"text/plain"`

            - `type: "text"`

              - `"text"`

          - `BetaContentBlockSource object { content, type }`

            - `content: string or array of BetaContentBlockSourceContent`

              - `string`

              - `BetaContentBlockSourceContent = array of BetaContentBlockSourceContent`

                - `BetaTextBlockParam object { text, type, cache_control, citations }`

                - `BetaImageBlockParam object { source, type, cache_control }`

            - `type: "content"`

              - `"content"`

          - `BetaURLPDFSource object { type, url }`

            - `type: "url"`

              - `"url"`

            - `url: string`

          - `BetaFileDocumentSource object { file_id, type }`

            - `file_id: string`

            - `type: "file"`

              - `"file"`

        - `type: "document"`

          - `"document"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `citations: optional BetaCitationsConfigParam`

          - `enabled: optional boolean`

        - `context: optional string`

        - `title: optional string`

      - `BetaSearchResultBlockParam object { content, source, title, 3 more }`

        - `content: array of BetaTextBlockParam`

          - `text: string`

          - `type: "text"`

          - `cache_control: optional BetaCacheControlEphemeral`

            Create a cache control breakpoint at this content block.

          - `citations: optional array of BetaTextCitationParam`

        - `source: string`

        - `title: string`

        - `type: "search_result"`

          - `"search_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `citations: optional BetaCitationsConfigParam`

      - `BetaThinkingBlockParam object { signature, thinking, type }`

        - `signature: string`

        - `thinking: string`

        - `type: "thinking"`

          - `"thinking"`

      - `BetaRedactedThinkingBlockParam object { data, type }`

        - `data: string`

        - `type: "redacted_thinking"`

          - `"redacted_thinking"`

      - `BetaToolUseBlockParam object { id, input, name, 3 more }`

        - `id: string`

        - `input: map[unknown]`

        - `name: string`

        - `type: "tool_use"`

          - `"tool_use"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120`

          Tool invocation directly from the model.

          - `BetaDirectCaller object { type }`

            Tool invocation directly from the model.

            - `type: "direct"`

              - `"direct"`

          - `BetaServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

            - `tool_id: string`

            - `type: "code_execution_20250825"`

              - `"code_execution_20250825"`

          - `BetaServerToolCaller20260120 object { tool_id, type }`

            - `tool_id: string`

            - `type: "code_execution_20260120"`

              - `"code_execution_20260120"`

      - `BetaToolResultBlockParam object { tool_use_id, type, cache_control, 2 more }`

        - `tool_use_id: string`

        - `type: "tool_result"`

          - `"tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `content: optional string or array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 2 more`

          - `string`

          - `array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 2 more`

            - `BetaTextBlockParam object { text, type, cache_control, citations }`

            - `BetaImageBlockParam object { source, type, cache_control }`

            - `BetaSearchResultBlockParam object { content, source, title, 3 more }`

            - `BetaRequestDocumentBlock object { source, type, cache_control, 3 more }`

            - `BetaToolReferenceBlockParam object { tool_name, type, cache_control }`

              Tool reference block that can be included in tool_result content.

              - `tool_name: string`

              - `type: "tool_reference"`

                - `"tool_reference"`

              - `cache_control: optional BetaCacheControlEphemeral`

                Create a cache control breakpoint at this content block.

        - `is_error: optional boolean`

      - `BetaServerToolUseBlockParam object { id, input, name, 3 more }`

        - `id: string`

        - `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"`

        - `type: "server_tool_use"`

          - `"server_tool_use"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120`

          Tool invocation directly from the model.

          - `BetaDirectCaller object { type }`

            Tool invocation directly from the model.

          - `BetaServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

          - `BetaServerToolCaller20260120 object { tool_id, type }`

      - `BetaWebSearchToolResultBlockParam object { content, tool_use_id, type, 2 more }`

        - `content: BetaWebSearchToolResultBlockParamContent`

          - `ResultBlock = array of BetaWebSearchResultBlockParam`

            - `encrypted_content: string`

            - `title: string`

            - `type: "web_search_result"`

              - `"web_search_result"`

            - `url: string`

            - `page_age: optional string`

          - `BetaWebSearchToolRequestError object { error_code, type }`

            - `error_code: BetaWebSearchToolResultErrorCode`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"max_uses_exceeded"`

              - `"too_many_requests"`

              - `"query_too_long"`

              - `"request_too_large"`

            - `type: "web_search_tool_result_error"`

              - `"web_search_tool_result_error"`

        - `tool_use_id: string`

        - `type: "web_search_tool_result"`

          - `"web_search_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120`

          Tool invocation directly from the model.

          - `BetaDirectCaller object { type }`

            Tool invocation directly from the model.

          - `BetaServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

          - `BetaServerToolCaller20260120 object { tool_id, type }`

      - `BetaWebFetchToolResultBlockParam object { content, tool_use_id, type, 2 more }`

        - `content: BetaWebFetchToolResultErrorBlockParam or BetaWebFetchBlockParam`

          - `BetaWebFetchToolResultErrorBlockParam object { error_code, type }`

            - `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"`

            - `type: "web_fetch_tool_result_error"`

              - `"web_fetch_tool_result_error"`

          - `BetaWebFetchBlockParam object { content, type, url, retrieved_at }`

            - `content: BetaRequestDocumentBlock`

            - `type: "web_fetch_result"`

              - `"web_fetch_result"`

            - `url: string`

              Fetched content URL

            - `retrieved_at: optional string`

              ISO 8601 timestamp when the content was retrieved

        - `tool_use_id: string`

        - `type: "web_fetch_tool_result"`

          - `"web_fetch_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120`

          Tool invocation directly from the model.

          - `BetaDirectCaller object { type }`

            Tool invocation directly from the model.

          - `BetaServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

          - `BetaServerToolCaller20260120 object { tool_id, type }`

      - `BetaAdvisorToolResultBlockParam object { content, tool_use_id, type, cache_control }`

        - `content: BetaAdvisorToolResultErrorParam or BetaAdvisorResultBlockParam or BetaAdvisorRedactedResultBlockParam`

          - `BetaAdvisorToolResultErrorParam object { error_code, type }`

            - `error_code: "max_uses_exceeded" or "prompt_too_long" or "too_many_requests" or 3 more`

              - `"max_uses_exceeded"`

              - `"prompt_too_long"`

              - `"too_many_requests"`

              - `"overloaded"`

              - `"unavailable"`

              - `"execution_time_exceeded"`

            - `type: "advisor_tool_result_error"`

              - `"advisor_tool_result_error"`

          - `BetaAdvisorResultBlockParam object { text, type, stop_reason }`

            - `text: string`

            - `type: "advisor_result"`

              - `"advisor_result"`

            - `stop_reason: optional string`

          - `BetaAdvisorRedactedResultBlockParam object { encrypted_content, type, stop_reason }`

            - `encrypted_content: string`

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

            - `type: "advisor_redacted_result"`

              - `"advisor_redacted_result"`

            - `stop_reason: optional string`

        - `tool_use_id: string`

        - `type: "advisor_tool_result"`

          - `"advisor_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaCodeExecutionToolResultBlockParam object { content, tool_use_id, type, cache_control }`

        - `content: BetaCodeExecutionToolResultBlockParamContent`

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

          - `BetaCodeExecutionToolResultErrorParam object { error_code, type }`

            - `error_code: BetaCodeExecutionToolResultErrorCode`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"too_many_requests"`

              - `"execution_time_exceeded"`

            - `type: "code_execution_tool_result_error"`

              - `"code_execution_tool_result_error"`

          - `BetaCodeExecutionResultBlockParam object { content, return_code, stderr, 2 more }`

            - `content: array of BetaCodeExecutionOutputBlockParam`

              - `file_id: string`

              - `type: "code_execution_output"`

                - `"code_execution_output"`

            - `return_code: number`

            - `stderr: string`

            - `stdout: string`

            - `type: "code_execution_result"`

              - `"code_execution_result"`

          - `BetaEncryptedCodeExecutionResultBlockParam object { content, encrypted_stdout, return_code, 2 more }`

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

            - `content: array of BetaCodeExecutionOutputBlockParam`

              - `file_id: string`

              - `type: "code_execution_output"`

            - `encrypted_stdout: string`

            - `return_code: number`

            - `stderr: string`

            - `type: "encrypted_code_execution_result"`

              - `"encrypted_code_execution_result"`

        - `tool_use_id: string`

        - `type: "code_execution_tool_result"`

          - `"code_execution_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaBashCodeExecutionToolResultBlockParam object { content, tool_use_id, type, cache_control }`

        - `content: BetaBashCodeExecutionToolResultErrorParam or BetaBashCodeExecutionResultBlockParam`

          - `BetaBashCodeExecutionToolResultErrorParam object { error_code, type }`

            - `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"`

            - `type: "bash_code_execution_tool_result_error"`

              - `"bash_code_execution_tool_result_error"`

          - `BetaBashCodeExecutionResultBlockParam object { content, return_code, stderr, 2 more }`

            - `content: array of BetaBashCodeExecutionOutputBlockParam`

              - `file_id: string`

              - `type: "bash_code_execution_output"`

                - `"bash_code_execution_output"`

            - `return_code: number`

            - `stderr: string`

            - `stdout: string`

            - `type: "bash_code_execution_result"`

              - `"bash_code_execution_result"`

        - `tool_use_id: string`

        - `type: "bash_code_execution_tool_result"`

          - `"bash_code_execution_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaTextEditorCodeExecutionToolResultBlockParam object { content, tool_use_id, type, cache_control }`

        - `content: BetaTextEditorCodeExecutionToolResultErrorParam or BetaTextEditorCodeExecutionViewResultBlockParam or BetaTextEditorCodeExecutionCreateResultBlockParam or BetaTextEditorCodeExecutionStrReplaceResultBlockParam`

          - `BetaTextEditorCodeExecutionToolResultErrorParam object { error_code, type, error_message }`

            - `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"`

            - `type: "text_editor_code_execution_tool_result_error"`

              - `"text_editor_code_execution_tool_result_error"`

            - `error_message: optional string`

          - `BetaTextEditorCodeExecutionViewResultBlockParam object { content, file_type, type, 3 more }`

            - `content: string`

            - `file_type: "text" or "image" or "pdf"`

              - `"text"`

              - `"image"`

              - `"pdf"`

            - `type: "text_editor_code_execution_view_result"`

              - `"text_editor_code_execution_view_result"`

            - `num_lines: optional number`

            - `start_line: optional number`

            - `total_lines: optional number`

          - `BetaTextEditorCodeExecutionCreateResultBlockParam object { is_file_update, type }`

            - `is_file_update: boolean`

            - `type: "text_editor_code_execution_create_result"`

              - `"text_editor_code_execution_create_result"`

          - `BetaTextEditorCodeExecutionStrReplaceResultBlockParam object { type, lines, new_lines, 3 more }`

            - `type: "text_editor_code_execution_str_replace_result"`

              - `"text_editor_code_execution_str_replace_result"`

            - `lines: optional array of string`

            - `new_lines: optional number`

            - `new_start: optional number`

            - `old_lines: optional number`

            - `old_start: optional number`

        - `tool_use_id: string`

        - `type: "text_editor_code_execution_tool_result"`

          - `"text_editor_code_execution_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaToolSearchToolResultBlockParam object { content, tool_use_id, type, cache_control }`

        - `content: BetaToolSearchToolResultErrorParam or BetaToolSearchToolSearchResultBlockParam`

          - `BetaToolSearchToolResultErrorParam object { error_code, type }`

            - `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"`

            - `type: "tool_search_tool_result_error"`

              - `"tool_search_tool_result_error"`

          - `BetaToolSearchToolSearchResultBlockParam object { tool_references, type }`

            - `tool_references: array of BetaToolReferenceBlockParam`

              - `tool_name: string`

              - `type: "tool_reference"`

              - `cache_control: optional BetaCacheControlEphemeral`

                Create a cache control breakpoint at this content block.

            - `type: "tool_search_tool_search_result"`

              - `"tool_search_tool_search_result"`

        - `tool_use_id: string`

        - `type: "tool_search_tool_result"`

          - `"tool_search_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaMCPToolUseBlockParam object { id, input, name, 3 more }`

        - `id: string`

        - `input: map[unknown]`

        - `name: string`

        - `server_name: string`

          The name of the MCP server

        - `type: "mcp_tool_use"`

          - `"mcp_tool_use"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaRequestMCPToolResultBlockParam object { tool_use_id, type, cache_control, 2 more }`

        - `tool_use_id: string`

        - `type: "mcp_tool_result"`

          - `"mcp_tool_result"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `content: optional string or array of BetaTextBlockParam`

          - `string`

          - `BetaMCPToolResultBlockParamContent = array of BetaTextBlockParam`

            - `text: string`

            - `type: "text"`

            - `cache_control: optional BetaCacheControlEphemeral`

              Create a cache control breakpoint at this content block.

            - `citations: optional array of BetaTextCitationParam`

        - `is_error: optional boolean`

      - `BetaContainerUploadBlockParam object { file_id, type, cache_control }`

        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.

        - `file_id: string`

        - `type: "container_upload"`

          - `"container_upload"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `BetaCompactionBlockParam object { type, cache_control, content, encrypted_content }`

        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"`

          - `"compaction"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `content: optional string`

          Summary of previously compacted content, or null if compaction failed

        - `encrypted_content: optional string`

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

      - `BetaMidConversationSystemBlockParam object { content, type, cache_control }`

        System instructions that appear mid-conversation.

        Use this block to provide or update system-level instructions at a specific
        point in the conversation, rather than only via the top-level `system` parameter.

        - `content: array of BetaTextBlockParam`

          System instruction text blocks.

          - `text: string`

          - `type: "text"`

          - `cache_control: optional BetaCacheControlEphemeral`

            Create a cache control breakpoint at this content block.

          - `citations: optional array of BetaTextCitationParam`

        - `type: "mid_conv_system"`

          - `"mid_conv_system"`

        - `cache_control: optional BetaCacheControlEphemeral`

          Create a cache control breakpoint at this content block.

  - `role: "user" or "assistant" or "system"`

    - `"user"`

    - `"assistant"`

    - `"system"`

- `model: Model`

  The model that will complete your prompt.

  See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

  - `"claude-opus-4-8" or "claude-opus-4-7" or "claude-mythos-preview" or 15 more`

    The model that will complete your prompt.

    See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

    - `"claude-opus-4-8"`

      Frontier intelligence for long-running agents and coding

    - `"claude-opus-4-7"`

      Frontier intelligence for long-running agents and coding

    - `"claude-mythos-preview"`

      New class of intelligence, strongest in coding and cybersecurity

    - `"claude-opus-4-6"`

      Frontier 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"`

      Premium model combining maximum intelligence with practical performance

    - `"claude-opus-4-5-20251101"`

      Premium model combining maximum intelligence with practical performance

    - `"claude-sonnet-4-5"`

      High-performance model for agents and coding

    - `"claude-sonnet-4-5-20250929"`

      High-performance model for agents and coding

    - `"claude-opus-4-1"`

      Exceptional model for specialized complex tasks

    - `"claude-opus-4-1-20250805"`

      Exceptional model for specialized complex tasks

    - `"claude-opus-4-0"`

      Powerful model for complex tasks

    - `"claude-opus-4-20250514"`

      Powerful model for complex tasks

    - `"claude-sonnet-4-0"`

      High-performance model with extended thinking

    - `"claude-sonnet-4-20250514"`

      High-performance model with extended thinking

    - `"claude-3-haiku-20240307"`

      Fast and cost-effective model

  - `string`

- `cache_control: optional BetaCacheControlEphemeral`

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

- `context_management: optional BetaContextManagementConfig`

  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

    - `BetaClearToolUses20250919Edit object { type, clear_at_least, clear_tool_inputs, 3 more }`

      - `type: "clear_tool_uses_20250919"`

        - `"clear_tool_uses_20250919"`

      - `clear_at_least: optional BetaInputTokensClearAtLeast`

        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"`

          - `"input_tokens"`

        - `value: number`

      - `clear_tool_inputs: optional boolean or array of string`

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

        - `boolean`

        - `array of string`

      - `exclude_tools: optional array of string`

        Tool names whose uses are preserved from clearing

      - `keep: optional BetaToolUsesKeep`

        Number of tool uses to retain in the conversation

        - `type: "tool_uses"`

          - `"tool_uses"`

        - `value: number`

      - `trigger: optional BetaInputTokensTrigger or BetaToolUsesTrigger`

        Condition that triggers the context management strategy

        - `BetaInputTokensTrigger object { type, value }`

          - `type: "input_tokens"`

            - `"input_tokens"`

          - `value: number`

        - `BetaToolUsesTrigger object { type, value }`

          - `type: "tool_uses"`

            - `"tool_uses"`

          - `value: number`

    - `BetaClearThinking20251015Edit object { type, keep }`

      - `type: "clear_thinking_20251015"`

        - `"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, value }`

          - `type: "thinking_turns"`

            - `"thinking_turns"`

          - `value: number`

        - `BetaAllThinkingTurns object { type }`

          - `type: "all"`

            - `"all"`

        - `"all"`

          - `"all"`

    - `BetaCompact20260112Edit object { type, instructions, pause_after_compaction, trigger }`

      Automatically compact older context when reaching the configured trigger threshold.

      - `type: "compact_20260112"`

        - `"compact_20260112"`

      - `instructions: optional string`

        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`

        When to trigger compaction. Defaults to 150000 input tokens.

- `mcp_servers: optional array of BetaRequestMCPServerURLDefinition`

  MCP servers to be utilized in this request

  - `name: string`

  - `type: "url"`

    - `"url"`

  - `url: string`

  - `authorization_token: optional string`

  - `tool_configuration: optional BetaRequestMCPServerToolConfiguration`

    - `allowed_tools: optional array of string`

    - `enabled: optional boolean`

- `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`

    All possible effort levels.

    - `"low"`

    - `"medium"`

    - `"high"`

    - `"xhigh"`

    - `"max"`

  - `format: optional BetaJSONOutputFormat`

    A schema to specify Claude's output format in responses. See [structured outputs](https://platform.claude.com/docs/en/build-with-claude/structured-outputs)

    - `schema: map[unknown]`

      The JSON schema of the format

    - `type: "json_schema"`

      - `"json_schema"`

  - `task_budget: optional BetaTokenTaskBudget`

    User-configurable total token budget across contexts.

    - `total: number`

      Total token budget across all contexts in the session.

    - `type: "tokens"`

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

      - `"tokens"`

    - `remaining: optional number`

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

- `output_format: optional BetaJSONOutputFormat`

  Deprecated: Use `output_config.format` instead. See [structured outputs](https://platform.claude.com/docs/en/build-with-claude/structured-outputs)

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

- `speed: optional "standard" or "fast"`

  The inference speed mode for this request. `"fast"` enables high output-tokens-per-second inference.

  - `"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](https://docs.claude.com/en/docs/system-prompts).

  - `string`

  - `array of BetaTextBlockParam`

    - `text: string`

    - `type: "text"`

    - `cache_control: optional BetaCacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional array of BetaTextCitationParam`

- `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](https://docs.claude.com/en/docs/build-with-claude/extended-thinking) for details.

  - `BetaThinkingConfigEnabled object { budget_tokens, type, display }`

    - `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](https://docs.claude.com/en/docs/build-with-claude/extended-thinking) for details.

    - `type: "enabled"`

      - `"enabled"`

    - `display: optional "summarized" or "omitted"`

      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"`

  - `BetaThinkingConfigDisabled object { type }`

    - `type: "disabled"`

      - `"disabled"`

  - `BetaThinkingConfigAdaptive object { type, display }`

    - `type: "adaptive"`

      - `"adaptive"`

    - `display: optional "summarized" or "omitted"`

      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"`

- `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 { type, disable_parallel_tool_use }`

    The model will automatically decide whether to use tools.

    - `type: "auto"`

      - `"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 { type, disable_parallel_tool_use }`

    The model will use any available tools.

    - `type: "any"`

      - `"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 { name, type, disable_parallel_tool_use }`

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

    - `name: string`

      The name of the tool to use.

    - `type: "tool"`

      - `"tool"`

    - `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 { type }`

    The model will not be allowed to use tools.

    - `type: "none"`

      - `"none"`

- `tools: optional array of BetaTool or BetaToolBash20241022 or BetaToolBash20250124 or 20 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](https://docs.claude.com/en/docs/agents-and-tools/tool-use/overview#server-tools), see their individual documentation as each has its own behavior (e.g., the [web search tool](https://docs.claude.com/en/docs/agents-and-tools/tool-use/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](https://json-schema.org/draft/2020-12) for the tool `input` shape that the model will produce in `tool_use` output content blocks.

  For example, if you defined `tools` as:

  ```json
  [
    {
      "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:

  ```json
  [
    {
      "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:

  ```json
  [
    {
      "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](https://docs.claude.com/en/docs/tool-use) for more details.

  - `BetaTool object { input_schema, name, allowed_callers, 7 more }`

    - `input_schema: object { type, properties, required }`

      [JSON schema](https://json-schema.org/draft/2020-12) for this tool's input.

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

      - `type: "object"`

        - `"object"`

      - `properties: optional map[unknown]`

      - `required: optional array of string`

    - `name: string`

      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"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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`

      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

    - `type: optional "custom"`

      - `"custom"`

  - `BetaToolBash20241022 object { name, type, allowed_callers, 4 more }`

    - `name: "bash"`

      Name of the tool.

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

      - `"bash"`

    - `type: "bash_20241022"`

      - `"bash_20241022"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { name, type, allowed_callers, 4 more }`

    - `name: "bash"`

      Name of the tool.

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

      - `"bash"`

    - `type: "bash_20250124"`

      - `"bash_20250124"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { name, type, allowed_callers, 3 more }`

    - `name: "code_execution"`

      Name of the tool.

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

      - `"code_execution"`

    - `type: "code_execution_20250522"`

      - `"code_execution_20250522"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { name, type, allowed_callers, 3 more }`

    - `name: "code_execution"`

      Name of the tool.

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

      - `"code_execution"`

    - `type: "code_execution_20250825"`

      - `"code_execution_20250825"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { name, type, allowed_callers, 3 more }`

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

    - `name: "code_execution"`

      Name of the tool.

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

      - `"code_execution"`

    - `type: "code_execution_20260120"`

      - `"code_execution_20260120"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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

  - `BetaToolComputerUse20241022 object { display_height_px, display_width_px, name, 7 more }`

    - `display_height_px: number`

      The height of the display in pixels.

    - `display_width_px: number`

      The width of the display in pixels.

    - `name: "computer"`

      Name of the tool.

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

      - `"computer"`

    - `type: "computer_20241022"`

      - `"computer_20241022"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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`

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

    - `input_examples: optional array of map[unknown]`

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

  - `BetaMemoryTool20250818 object { name, type, allowed_callers, 4 more }`

    - `name: "memory"`

      Name of the tool.

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

      - `"memory"`

    - `type: "memory_20250818"`

      - `"memory_20250818"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { display_height_px, display_width_px, name, 7 more }`

    - `display_height_px: number`

      The height of the display in pixels.

    - `display_width_px: number`

      The width of the display in pixels.

    - `name: "computer"`

      Name of the tool.

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

      - `"computer"`

    - `type: "computer_20250124"`

      - `"computer_20250124"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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`

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

    - `input_examples: optional array of map[unknown]`

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

  - `BetaToolTextEditor20241022 object { name, type, allowed_callers, 4 more }`

    - `name: "str_replace_editor"`

      Name of the tool.

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

      - `"str_replace_editor"`

    - `type: "text_editor_20241022"`

      - `"text_editor_20241022"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { display_height_px, display_width_px, name, 8 more }`

    - `display_height_px: number`

      The height of the display in pixels.

    - `display_width_px: number`

      The width of the display in pixels.

    - `name: "computer"`

      Name of the tool.

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

      - `"computer"`

    - `type: "computer_20251124"`

      - `"computer_20251124"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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`

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

    - `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

  - `BetaToolTextEditor20250124 object { name, type, allowed_callers, 4 more }`

    - `name: "str_replace_editor"`

      Name of the tool.

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

      - `"str_replace_editor"`

    - `type: "text_editor_20250124"`

      - `"text_editor_20250124"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { name, type, allowed_callers, 4 more }`

    - `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.

      - `"str_replace_based_edit_tool"`

    - `type: "text_editor_20250429"`

      - `"text_editor_20250429"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { name, type, allowed_callers, 5 more }`

    - `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.

      - `"str_replace_based_edit_tool"`

    - `type: "text_editor_20250728"`

      - `"text_editor_20250728"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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`

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

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

  - `BetaWebSearchTool20250305 object { name, type, allowed_callers, 7 more }`

    - `name: "web_search"`

      Name of the tool.

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

      - `"web_search"`

    - `type: "web_search_20250305"`

      - `"web_search_20250305"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: optional array of string`

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

    - `blocked_domains: optional array of string`

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

    - `cache_control: optional BetaCacheControlEphemeral`

      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`

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

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

    - `user_location: optional BetaUserLocation`

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

      - `type: "approximate"`

        - `"approximate"`

      - `city: optional string`

        The city of the user.

      - `country: optional string`

        The two letter [ISO country code](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2) of the user.

      - `region: optional string`

        The region of the user.

      - `timezone: optional string`

        The [IANA timezone](https://nodatime.org/TimeZones) of the user.

  - `BetaWebFetchTool20250910 object { name, type, allowed_callers, 8 more }`

    - `name: "web_fetch"`

      Name of the tool.

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

      - `"web_fetch"`

    - `type: "web_fetch_20250910"`

      - `"web_fetch_20250910"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: optional array of string`

      List of domains to allow fetching from

    - `blocked_domains: optional array of string`

      List of domains to block fetching from

    - `cache_control: optional BetaCacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional BetaCitationsConfigParam`

      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`

      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.

    - `max_uses: optional number`

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

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

  - `BetaWebSearchTool20260209 object { name, type, allowed_callers, 7 more }`

    - `name: "web_search"`

      Name of the tool.

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

      - `"web_search"`

    - `type: "web_search_20260209"`

      - `"web_search_20260209"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: optional array of string`

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

    - `blocked_domains: optional array of string`

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

    - `cache_control: optional BetaCacheControlEphemeral`

      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`

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

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

    - `user_location: optional BetaUserLocation`

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

  - `BetaWebFetchTool20260209 object { name, type, allowed_callers, 8 more }`

    - `name: "web_fetch"`

      Name of the tool.

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

      - `"web_fetch"`

    - `type: "web_fetch_20260209"`

      - `"web_fetch_20260209"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: optional array of string`

      List of domains to allow fetching from

    - `blocked_domains: optional array of string`

      List of domains to block fetching from

    - `cache_control: optional BetaCacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional BetaCitationsConfigParam`

      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`

      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.

    - `max_uses: optional number`

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

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

  - `BetaWebFetchTool20260309 object { name, type, allowed_callers, 9 more }`

    Web fetch tool with use_cache parameter for bypassing cached content.

    - `name: "web_fetch"`

      Name of the tool.

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

      - `"web_fetch"`

    - `type: "web_fetch_20260309"`

      - `"web_fetch_20260309"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: optional array of string`

      List of domains to allow fetching from

    - `blocked_domains: optional array of string`

      List of domains to block fetching from

    - `cache_control: optional BetaCacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional BetaCitationsConfigParam`

      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`

      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.

    - `max_uses: optional number`

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

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

    - `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 { model, name, type, 6 more }`

    - `model: Model`

      The model that will complete your prompt.

      See [models](https://docs.anthropic.com/en/docs/models-overview) 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.

      - `"advisor"`

    - `type: "advisor_20260301"`

      - `"advisor_20260301"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `caching: optional BetaCacheControlEphemeral`

      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_uses: optional number`

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

    - `strict: optional boolean`

      When true, guarantees schema validation on tool names and inputs

  - `BetaToolSearchToolBm25_20251119 object { name, type, allowed_callers, 3 more }`

    - `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.

      - `"tool_search_tool_bm25"`

    - `type: "tool_search_tool_bm25_20251119" or "tool_search_tool_bm25"`

      - `"tool_search_tool_bm25_20251119"`

      - `"tool_search_tool_bm25"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { name, type, allowed_callers, 3 more }`

    - `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.

      - `"tool_search_tool_regex"`

    - `type: "tool_search_tool_regex_20251119" or "tool_search_tool_regex"`

      - `"tool_search_tool_regex_20251119"`

      - `"tool_search_tool_regex"`

    - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: optional BetaCacheControlEphemeral`

      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 { mcp_server_name, type, cache_control, 2 more }`

    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.

    - `mcp_server_name: string`

      Name of the MCP server to configure tools for

    - `type: "mcp_toolset"`

      - `"mcp_toolset"`

    - `cache_control: optional BetaCacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `configs: optional map[BetaMCPToolConfig]`

      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`

### Returns

- `BetaMessageTokensCount object { context_management, input_tokens }`

  - `context_management: BetaCountTokensContextManagementResponse`

    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

```http
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-4-6\",
          \"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

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