# Cartesia API

Category: [Speech, image and audio](https://free-web-services.com/web-services/ai/media/)  
Page: https://free-web-services.com/web-services/ai/media/cartesia-api.html  
Documentation: https://docs.cartesia.ai/api-reference/tts/bytes

The Cartesia API offers fast text-to-speech and speech-to-text, for example to give a voice agent spoken answers. A POST request with a JSON body (model, transcript, voice, output format) returns WAV, MP3 or raw audio; SSE and WebSocket streaming are also available. Requests need an Authorization: Bearer and a Cartesia-Version header. Free plan with 20,000 credits per month (text-to-speech uses about one credit per character); a commercial use license comes with paid plans. An official MCP server at https://mcp.cartesia.ai/mcp lets AI agents generate speech, transcribe audio and manage voices.

- API key: Needed, free
- Pricing: Free plan with 20,000 credits per month (text-to-speech uses about one credit per character); a commercial use license comes with paid plans.
- Commercial use: Not on the free plan
- From the browser: Yes (CORS)
- Formats: JSON
- Interface: REST, MCP
- Provider: docs.cartesia.ai
- Last checked: Working on November 3rd, 2026

Example request:

```sh
curl -X POST 'https://api.cartesia.ai/tts/bytes' \
  -H 'Authorization: Bearer YOUR_API_KEY' \
  -H 'Cartesia-Version: 2026-08-14' \
  -H 'Content-Type: application/json' \
  -d '{"model_id":"sonic-3","transcript":"Hello, world!","voice":{"mode":"id","id":"db6b0ed5-d5d3-463d-ae85-518a07d3c2b4"},"output_format":{"container":"mp3","sample_rate":44100,"bit_rate":128000}}'
```

Replace YOUR_API_KEY with your own key. The JavaScript works in a web page as well as in Node.js 18 or newer.