Cartesia API

Name: Cartesia API API
Brand: Cartesia API
Availability: InStock

★ Only Publicly Available OpenAPI DocumentAI/MLSpeechbearer3 EndpointsREST

For Agents

Synthesize speech from text and transcribe audio files using Cartesia's Sonic and Ink voice models, with streaming output for low-latency agent voice.

Quickstart

Get started with Cartesia API in minutes using your preferred integration method.

# Add to your MCP client config (Claude Desktop, Cursor, Windsurf)
{
  "jentic": {
    "url": "https://api.jentic.com/mcp",
    "auth": "oauth"
  }
}

# Then ask your agent:
"synthesize speech with cartesia"

# → Jentic returns the GET /events tool with parameter schema, agent executes.

Capabilities

What an agent can do with Cartesia API API.

Synthesize text into raw audio bytes via Sonic TTS for batch playback

Stream synthesized speech as server-sent events for sub-second voice agent responses

Transcribe uploaded audio files into text using the Ink speech-to-text model

Select voice, language, and output sample rate per text-to-speech request

GET STARTED

Start building with Cartesia API API

Explore with Jentic

View OpenAPI Document

Jentic publishes the only available OpenAPI document for Cartesia API, keeping it validated and agent-ready.

Jentic publishes the only available OpenAPI specification for Cartesia API, keeping it validated and agent-ready. Cartesia provides ultra-fast, realistic voice AI for text-to-speech and speech-to-text using the Sonic model family for synthesis and the Ink model family for transcription. The API supports both raw byte responses and server-sent event streaming for low-latency TTS, plus file-based audio upload for STT. It is designed for real-time agent voices, conversational interfaces, and audio content production where sub-second first-token latency matters.

Use Cases

Patterns agents use Cartesia API API for, with concrete tasks.

★ Real-time voice agent responses

Stream synthesized speech to a voice agent or phone assistant via the /tts/sse endpoint so the user hears the first audio chunk in well under a second. Sonic generates audio incrementally as the LLM produces tokens, keeping conversation natural without long silences. Suited to support bots, IVR replacements, and interactive voice experiences.

POST to /tts/sse with the assistant's reply text, voice id, and language=en, then forward the streaming audio chunks to the caller as they arrive.

Batch audio narration

Use POST /tts/bytes to render scripted text into a complete audio file in a single response, suitable for podcasts, e-learning narration, audiobook chapters, or pre-recorded prompts. The byte endpoint returns the full clip once synthesis completes, which is simpler to handle than streaming for offline rendering.

Call POST /tts/bytes with a 500-word script, voice id, and 24000 Hz output, then save the returned audio bytes as narration.mp3.

Call recording transcription

Upload recorded audio files to /stt to obtain text transcripts using the Ink model. Useful for call summarization, meeting notes, voice note search, and feeding spoken content back into LLM workflows.

POST a meeting.wav file to /stt and store the returned transcript text against the meeting record.

AI voice agent integration via Jentic

Agents using Jentic search by intent ('synthesize speech') and load the Cartesia /tts/sse schema, then execute the call with the bearer token managed inside the Jentic vault. This avoids hand-coding streaming SSE clients and keeps Cartesia credentials out of the agent's prompt.

Search Jentic for 'synthesize speech with cartesia', load the /tts/sse operation, and execute it with the supplied script to return streaming audio.

Key Endpoints

3 endpoints — jentic publishes the only available openapi specification for cartesia api, keeping it validated and agent-ready.

METHOD

PATH

DESCRIPTION

POST

/tts/bytes

Synthesize text to a complete audio byte payload

POST

/tts/sse

Stream synthesized speech as server-sent events

POST

/stt

Transcribe an uploaded audio file into text

POST

/tts/bytes

Synthesize text to a complete audio byte payload

POST

/tts/sse

Stream synthesized speech as server-sent events

POST

/stt

Transcribe an uploaded audio file into text

Why though Jentic?

Three things that make agents converge on Jentic-routed access.

Credential isolation

Cartesia bearer API keys are stored encrypted in the Jentic vault (MAXsystem). Agents receive scoped access at execution time and the raw key never enters the prompt or logs.

Intent-based discovery

Agents search by intent (e.g., 'synthesize speech' or 'transcribe audio') and Jentic returns the matching Cartesia operation along with its input schema, so the agent calls the right TTS or STT endpoint without browsing docs.

Time to first call

Direct Cartesia integration including SSE streaming and key handling: 1-2 days. Through Jentic: under 30 minutes — search, load, execute.

Related APIs

Alternatives and complements available in the Jentic catalogue.

Alternative

ElevenLabs API

ElevenLabs offers similar realistic TTS and voice cloning with a larger voice library.

Choose ElevenLabs when voice cloning or a wider stock voice catalog matters more than first-token latency.

Complementary

OpenAI API

Pair OpenAI's chat models with Cartesia to convert generated replies into streamed speech.

Use OpenAI for the language model layer and Cartesia for the voice rendering layer in a single voice agent pipeline.

Alternative

Deepgram API

Deepgram is a competing speech-to-text provider with real-time streaming transcription.

Choose Deepgram when you need streaming STT or diarization that the file-based Cartesia /stt endpoint does not currently expose.

FAQs

Specific to using Cartesia API API through Jentic.

Why is there no official OpenAPI spec for Cartesia API?

Cartesia does not publish an OpenAPI specification. Jentic generates and maintains this spec so that AI agents and developers can call Cartesia API via structured tooling. It is validated against the live API and kept up to date. Get started at https://app.jentic.com/sign-up.

What authentication does the Cartesia API use?

The Cartesia API uses HTTP bearer token authentication. You pass your Cartesia API key as a Bearer token in the Authorization header. Through Jentic, the key is stored encrypted in the MAXsystem vault and never exposed to the agent's prompt context.

Can I stream text-to-speech output instead of waiting for the full file?

Yes. POST to /tts/sse to receive synthesized audio as server-sent events, with the first chunk arriving in well under a second. Use /tts/bytes when you want the complete audio payload returned in a single response.

What audio inputs does the Cartesia speech-to-text endpoint accept?

The /stt endpoint accepts uploaded audio files for transcription using the Ink model family. You send the file as a multipart form upload and receive transcript text in the response.

What are the rate limits for the Cartesia API?

Cartesia does not publish rate limits in this OpenAPI spec; quotas depend on your account plan. Check your Cartesia dashboard at https://docs.cartesia.ai for current limits and upgrade options.

How do I synthesize speech with Cartesia through Jentic?

Run pip install jentic, then search Jentic with the query 'synthesize speech with cartesia', load the /tts/sse or /tts/bytes operation schema, and execute it with your text and voice id. Jentic injects the Cartesia bearer token from the vault at execution time.