📄 claude/api/messages-count-tokens

File: messages-count-tokens.md | Updated: 11/15/2025

Source: https://docs.claude.com/en/api/messages-count-tokens

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Count Message tokens

Home Developer Guide API Reference Model Context Protocol (MCP) Resources Release Notes

cURL

cURL

Copy

curl https://api.anthropic.com/v1/messages/count_tokens \
     --header "x-api-key: $ANTHROPIC_API_KEY" \
     --header "anthropic-version: 2023-06-01" \
     --header "content-type: application/json" \
     --data \
'{
    "model": "claude-3-7-sonnet-20250219",
    "messages": [\
        {"role": "user", "content": "Hello, world"}\
    ]
}'

200

4XX

Copy

{
  "input_tokens": 2095
}

POST

/

v1

/

messages

/

count_tokens

cURL

cURL

Copy

curl https://api.anthropic.com/v1/messages/count_tokens \
     --header "x-api-key: $ANTHROPIC_API_KEY" \
     --header "anthropic-version: 2023-06-01" \
     --header "content-type: application/json" \
     --data \
'{
    "model": "claude-3-7-sonnet-20250219",
    "messages": [\
        {"role": "user", "content": "Hello, world"}\
    ]
}'

200

4XX

Copy

{
  "input_tokens": 2095
}

Headers

​

anthropic-beta

string[]

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

To use multiple betas, use a comma separated list like beta1,beta2 or specify the header multiple times for each beta.

​

anthropic-version

string

required

The version of the Claude API you want to use.

Read more about versioning and our version history here .

​

x-api-key

string

required

Your unique API key for authentication.

This key is required in the header of all API requests, to authenticate your account and access Anthropic's services. Get your API key through the Console . Each key is scoped to a Workspace.

Body

application/json

​

messages

InputMessage · object[]

required

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:

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

Example with multiple conversational turns:

[  {"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:

[  {"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:

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

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

See input examples .

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

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

Show child attributes

​

model

string

required

The model that will complete your prompt.

See models for additional details and options.

Required string length: 1 - 256

Examples:

"claude-sonnet-4-5-20250929"

​

context_management

object | null

Context management configuration.

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

Show child attributes

​

mcp_servers

RequestMCPServerURLDefinition · object[]

MCP servers to be utilized in this request

Maximum length: 20

Show child attributes

​

system

stringText · object[]

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 .

Examples:

[  {    "text": "Today's date is 2024-06-01.",    "type": "text"  }]

"Today's date is 2023-01-01."

​

thinking

object

Configuration for enabling Claude's extended thinking.

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

See extended thinking for details.

  • Enabled
  • Disabled

Show child attributes

​

tool_choice

object

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. The model will automatically decide whether to use tools.

  • Auto
  • Any
  • Tool
  • None

Show child attributes

​

tools

Tools · array

Definitions of tools that the model may use.

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

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

Each tool definition includes:

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

For example, if you defined tools as:

[  {    "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:

[  {    "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:

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

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

See our guide for more details.

  • Custom tool
  • Bash tool (2024-10-22)
  • Bash tool (2025-01-24)
  • Code execution tool (2025-05-22)
  • CodeExecutionTool_20250825
  • Computer use tool (2024-01-22)
  • MemoryTool_20250818
  • Computer use tool (2025-01-24)
  • Text editor tool (2024-10-22)
  • Text editor tool (2025-01-24)
  • Text editor tool (2025-04-29)
  • TextEditor_20250728
  • Web search tool (2025-03-05)
  • WebFetchTool_20250910

Show child attributes

Examples:

{  "description": "Get the current weather in a given location",  "input_schema": {    "properties": {      "location": {        "description": "The city and state, e.g. San Francisco, CA",        "type": "string"      },      "unit": {        "description": "Unit for the output - one of (celsius, fahrenheit)",        "type": "string"      }    },    "required": ["location"],    "type": "object"  },  "name": "get_weather"}

Response

200

application/json

Successful Response

​

context_management

object | null

required

Information about context management applied to the message.

Show child attributes

​

input_tokens

integer

required

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

Examples:

2095

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