> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nano-gpt.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Messages Count Tokens

> Anthropic-compatible token estimate endpoint for planning and cost control

## Overview

Use `POST /api/v1/messages/count_tokens` to estimate the number of input tokens for an Anthropic Messages-format request.

This endpoint is useful for request planning, context budgeting, and cost control. The result is an estimate and may not exactly match a provider tokenizer.

## Endpoint

```text theme={null}
POST https://nano-gpt.com/api/v1/messages/count_tokens
```

## Authentication

Use either header:

* `Authorization: Bearer YOUR_API_KEY`
* `x-api-key: YOUR_API_KEY`

## Request Body

```json theme={null}
{
  "model": "claude-3-5-sonnet",
  "system": "You are concise.",
  "messages": [
    {
      "role": "user",
      "content": "Hello"
    }
  ],
  "tools": [],
  "tool_choice": null
}
```

## Supported Content

The request uses Anthropic message format and supports:

* text blocks
* image and document-like blocks
* tool use blocks
* tool result blocks
* `system`
* `tools`
* `tool_choice`

## Response

```json theme={null}
{
  "input_tokens": 123
}
```

## Example

```bash theme={null}
curl -X POST https://nano-gpt.com/api/v1/messages/count_tokens \
  -H "Authorization: Bearer $NANOGPT_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-3-5-sonnet",
    "system": "You are concise.",
    "messages": [
      { "role": "user", "content": "Hello" }
    ]
  }'
```

## Notes

* This is an estimate for planning and cost control.
* It may not exactly match a provider tokenizer.
* For generation, use `POST /api/v1/messages`.