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Last updated: 2026-06-06

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Claude Token Counting

POST /v1/messages/count_tokens
Use this endpoint to estimate input token usage before you send the real POST /v1/messages request. It is useful for Claude CLI, Claude Code, budget checks, and context-trimming logic.

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Authentication

The recommended headers follow Anthropic-style requests: 
x-api-key: YOUR_API_KEY
anthropic-version: 2023-06-01
Standard Bearer authentication also works, but Anthropic ecosystem clients usually send the headers above.

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Request Body

The body follows the Claude Messages shape. The smallest practical request usually includes:
  • model
  • messages
If your request also includes system, tools, tool results, or text content, those are included in the estimate too.

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Request Example

curl https://api.crazyrouter.com/v1/messages/count_tokens   -H "Content-Type: application/json"   -H "x-api-key: YOUR_API_KEY"   -H "anthropic-version: 2023-06-01"   -d '{
    "model": "claude-opus-4-8",
    "messages": [
      {"role": "user", "content": "hello"}
    ]
  }'

import requests

resp = requests.post(
    "https://api.crazyrouter.com/v1/messages/count_tokens",
    headers={
        "x-api-key": "YOUR_API_KEY",
        "anthropic-version": "2023-06-01",
        "Content-Type": "application/json",
    },
    json={
        "model": "claude-opus-4-8",
        "messages": [
            {"role": "user", "content": "hello"}
        ],
    },
)

print(resp.json())

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Response Example

{
  "input_tokens": 4
}

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Response Fields

FieldTypeDescription
input_tokensintegerEstimated input tokens for the text portion of the request
warningstringOptional warning; may appear when images or files were not included in the estimate

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Current Limits

The current implementation mainly estimates:
  • system
  • text content in messages
  • text and JSON content in tool definitions and tool results
If the request contains images or files, those image/file tokens are not included in input_tokens. In that case the response may include a warning, and real billing can be higher than this estimate.
This endpoint returns an estimate, not a final billing record. Actual usage is determined by the real model call.