## 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)

### Body Parameters

- `messages: array of MessageParam`

  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 ContentBlockParam`

    - `string`

    - `array of ContentBlockParam`

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

        - `text: string`

        - `type: "text"`

          - `"text"`

        - `cache_control: optional CacheControlEphemeral`

          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 TextCitationParam`

          - `CitationCharLocationParam 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"`

          - `CitationPageLocationParam 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"`

          - `CitationContentBlockLocationParam 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"`

          - `CitationWebSearchResultLocationParam 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`

          - `CitationSearchResultLocationParam 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"`

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

        - `source: Base64ImageSource or URLImageSource`

          - `Base64ImageSource 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"`

          - `URLImageSource object { type, url }`

            - `type: "url"`

              - `"url"`

            - `url: string`

        - `type: "image"`

          - `"image"`

        - `cache_control: optional CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

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

        - `source: Base64PDFSource or PlainTextSource or ContentBlockSource or URLPDFSource`

          - `Base64PDFSource object { data, media_type, type }`

            - `data: string`

            - `media_type: "application/pdf"`

              - `"application/pdf"`

            - `type: "base64"`

              - `"base64"`

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

            - `data: string`

            - `media_type: "text/plain"`

              - `"text/plain"`

            - `type: "text"`

              - `"text"`

          - `ContentBlockSource object { content, type }`

            - `content: string or array of ContentBlockSourceContent`

              - `string`

              - `ContentBlockSourceContent = array of ContentBlockSourceContent`

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

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

            - `type: "content"`

              - `"content"`

          - `URLPDFSource object { type, url }`

            - `type: "url"`

              - `"url"`

            - `url: string`

        - `type: "document"`

          - `"document"`

        - `cache_control: optional CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `citations: optional CitationsConfigParam`

          - `enabled: optional boolean`

        - `context: optional string`

        - `title: optional string`

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

        - `content: array of TextBlockParam`

          - `text: string`

          - `type: "text"`

          - `cache_control: optional CacheControlEphemeral`

            Create a cache control breakpoint at this content block.

          - `citations: optional array of TextCitationParam`

        - `source: string`

        - `title: string`

        - `type: "search_result"`

          - `"search_result"`

        - `cache_control: optional CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `citations: optional CitationsConfigParam`

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

        - `signature: string`

        - `thinking: string`

        - `type: "thinking"`

          - `"thinking"`

      - `RedactedThinkingBlockParam object { data, type }`

        - `data: string`

        - `type: "redacted_thinking"`

          - `"redacted_thinking"`

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

        - `id: string`

        - `input: map[unknown]`

        - `name: string`

        - `type: "tool_use"`

          - `"tool_use"`

        - `cache_control: optional CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120`

          Tool invocation directly from the model.

          - `DirectCaller object { type }`

            Tool invocation directly from the model.

            - `type: "direct"`

              - `"direct"`

          - `ServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

            - `tool_id: string`

            - `type: "code_execution_20250825"`

              - `"code_execution_20250825"`

          - `ServerToolCaller20260120 object { tool_id, type }`

            - `tool_id: string`

            - `type: "code_execution_20260120"`

              - `"code_execution_20260120"`

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

        - `tool_use_id: string`

        - `type: "tool_result"`

          - `"tool_result"`

        - `cache_control: optional CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `content: optional string or array of TextBlockParam or ImageBlockParam or SearchResultBlockParam or 2 more`

          - `string`

          - `array of TextBlockParam or ImageBlockParam or SearchResultBlockParam or 2 more`

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

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

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

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

            - `ToolReferenceBlockParam 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 CacheControlEphemeral`

                Create a cache control breakpoint at this content block.

        - `is_error: optional boolean`

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

        - `id: string`

        - `input: map[unknown]`

        - `name: "web_search" or "web_fetch" or "code_execution" or 4 more`

          - `"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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120`

          Tool invocation directly from the model.

          - `DirectCaller object { type }`

            Tool invocation directly from the model.

          - `ServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

          - `ServerToolCaller20260120 object { tool_id, type }`

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

        - `content: WebSearchToolResultBlockParamContent`

          - `WebSearchToolResultBlockItem = array of WebSearchResultBlockParam`

            - `encrypted_content: string`

            - `title: string`

            - `type: "web_search_result"`

              - `"web_search_result"`

            - `url: string`

            - `page_age: optional string`

          - `WebSearchToolRequestError object { error_code, type }`

            - `error_code: WebSearchToolResultErrorCode`

              - `"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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120`

          Tool invocation directly from the model.

          - `DirectCaller object { type }`

            Tool invocation directly from the model.

          - `ServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

          - `ServerToolCaller20260120 object { tool_id, type }`

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

        - `content: WebFetchToolResultErrorBlockParam or WebFetchBlockParam`

          - `WebFetchToolResultErrorBlockParam object { error_code, type }`

            - `error_code: WebFetchToolResultErrorCode`

              - `"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"`

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

            - `content: DocumentBlockParam`

            - `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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

        - `caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120`

          Tool invocation directly from the model.

          - `DirectCaller object { type }`

            Tool invocation directly from the model.

          - `ServerToolCaller object { tool_id, type }`

            Tool invocation generated by a server-side tool.

          - `ServerToolCaller20260120 object { tool_id, type }`

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

        - `content: CodeExecutionToolResultBlockParamContent`

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

          - `CodeExecutionToolResultErrorParam object { error_code, type }`

            - `error_code: CodeExecutionToolResultErrorCode`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"too_many_requests"`

              - `"execution_time_exceeded"`

            - `type: "code_execution_tool_result_error"`

              - `"code_execution_tool_result_error"`

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

            - `content: array of CodeExecutionOutputBlockParam`

              - `file_id: string`

              - `type: "code_execution_output"`

                - `"code_execution_output"`

            - `return_code: number`

            - `stderr: string`

            - `stdout: string`

            - `type: "code_execution_result"`

              - `"code_execution_result"`

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

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

            - `content: array of CodeExecutionOutputBlockParam`

              - `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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

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

        - `content: BashCodeExecutionToolResultErrorParam or BashCodeExecutionResultBlockParam`

          - `BashCodeExecutionToolResultErrorParam object { error_code, type }`

            - `error_code: BashCodeExecutionToolResultErrorCode`

              - `"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"`

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

            - `content: array of BashCodeExecutionOutputBlockParam`

              - `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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

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

        - `content: TextEditorCodeExecutionToolResultErrorParam or TextEditorCodeExecutionViewResultBlockParam or TextEditorCodeExecutionCreateResultBlockParam or TextEditorCodeExecutionStrReplaceResultBlockParam`

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

            - `error_code: TextEditorCodeExecutionToolResultErrorCode`

              - `"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`

          - `TextEditorCodeExecutionViewResultBlockParam 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`

          - `TextEditorCodeExecutionCreateResultBlockParam object { is_file_update, type }`

            - `is_file_update: boolean`

            - `type: "text_editor_code_execution_create_result"`

              - `"text_editor_code_execution_create_result"`

          - `TextEditorCodeExecutionStrReplaceResultBlockParam 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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

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

        - `content: ToolSearchToolResultErrorParam or ToolSearchToolSearchResultBlockParam`

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

            - `error_code: ToolSearchToolResultErrorCode`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"too_many_requests"`

              - `"execution_time_exceeded"`

            - `type: "tool_search_tool_result_error"`

              - `"tool_search_tool_result_error"`

            - `error_message: optional string`

          - `ToolSearchToolSearchResultBlockParam object { tool_references, type }`

            - `tool_references: array of ToolReferenceBlockParam`

              - `tool_name: string`

              - `type: "tool_reference"`

              - `cache_control: optional CacheControlEphemeral`

                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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `ContainerUploadBlockParam 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 CacheControlEphemeral`

          Create a cache control breakpoint at this content block.

      - `MidConversationSystemBlockParam 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 TextBlockParam`

          System instruction text blocks.

          - `text: string`

          - `type: "text"`

          - `cache_control: optional CacheControlEphemeral`

            Create a cache control breakpoint at this content block.

          - `citations: optional array of TextCitationParam`

        - `type: "mid_conv_system"`

          - `"mid_conv_system"`

        - `cache_control: optional CacheControlEphemeral`

          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-fable-5" or "claude-mythos-5" or "claude-opus-4-8" or 17 more`

    The model that will complete your prompt.

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

    - `"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-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 CacheControlEphemeral`

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

- `output_config: optional OutputConfig`

  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 JSONOutputFormat`

    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"`

- `system: optional string or array of TextBlockParam`

  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 TextBlockParam`

    - `text: string`

    - `type: "text"`

    - `cache_control: optional CacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional array of TextCitationParam`

- `thinking: optional ThinkingConfigParam`

  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.

  - `ThinkingConfigEnabled 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"`

  - `ThinkingConfigDisabled object { type }`

    - `type: "disabled"`

      - `"disabled"`

  - `ThinkingConfigAdaptive 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 ToolChoice`

  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.

  - `ToolChoiceAuto 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.

  - `ToolChoiceAny 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.

  - `ToolChoiceTool 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.

  - `ToolChoiceNone object { type }`

    The model will not be allowed to use tools.

    - `type: "none"`

      - `"none"`

- `tools: optional array of MessageCountTokensTool`

  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.

  - `Tool 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 CacheControlEphemeral`

      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"`

  - `ToolBash20250124 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 CacheControlEphemeral`

      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

  - `CodeExecutionTool20250522 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 CacheControlEphemeral`

      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

  - `CodeExecutionTool20250825 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 CacheControlEphemeral`

      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

  - `CodeExecutionTool20260120 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 CacheControlEphemeral`

      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

  - `MemoryTool20250818 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 CacheControlEphemeral`

      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

  - `ToolTextEditor20250124 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 CacheControlEphemeral`

      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

  - `ToolTextEditor20250429 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 CacheControlEphemeral`

      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

  - `ToolTextEditor20250728 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 CacheControlEphemeral`

      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

  - `WebSearchTool20250305 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 CacheControlEphemeral`

      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 UserLocation`

      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.

  - `WebFetchTool20250910 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 CacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional CitationsConfigParam`

      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

  - `WebSearchTool20260209 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 CacheControlEphemeral`

      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 UserLocation`

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

  - `WebFetchTool20260209 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 CacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional CitationsConfigParam`

      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

  - `WebFetchTool20260309 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 CacheControlEphemeral`

      Create a cache control breakpoint at this content block.

    - `citations: optional CitationsConfigParam`

      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.

  - `ToolSearchToolBm25_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 CacheControlEphemeral`

      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

  - `ToolSearchToolRegex20251119 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 CacheControlEphemeral`

      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

### Returns

- `MessageTokensCount object { input_tokens }`

  - `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
{
  "input_tokens": 2095
}
```
