Agent-ready OpenAPI document · curated by JenticAI/MLSpeechbearer3 EndpointsREST
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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.
Use for: I need to convert a chatbot reply into spoken audio, Stream a voice agent response with minimal first-token latency, Transcribe a recorded customer call into text, Generate a podcast voiceover from a written script
Not supported: Does not handle voice cloning, real-time STT streaming, or audio editing - use for Sonic text-to-speech and Ink file transcription only.
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.
Install Jentic One Beta
Connect the Cartesia API to your agent
Jentic One is a self-hosted execution layer for AI agents. It lets your agent call the Cartesia API, or any other public or private API you need. You set the rules, the agent never sees your credentials, and every call is logged.
Two steps, two machines. Install the instance in a safe environment, then register your agent from wherever it runs.
1
Step 1: Jentic One Host machine
# On the machine that will host your Jentic One instance:
curl -fsSL "https://jentic.com/install.sh?src=apis&api=%2Fapis%2Fcartesia.ai%2Fcartesia" | sh2
Step 2: Agent machine
# On the machine where your agent runs (keep this separate from the instance):
curl -fsSL "https://jentic.com/install.sh?src=apis&api=%2Fapis%2Fcartesia.ai%2Fcartesia" | sh
jentic register # connects your agent to your Jentic One instanceJentic One is in public beta. The setup above keeps your agent separate from the instance, which is what you want before using real credentials: an agent running as the same OS user as Jentic One can read its stored keys directly. Just evaluating? A single local install is fine to start. See the secure deployment guide for the tiers.
Capabilities
What an agent can do with Cartesia 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
Authenticate with a Cartesia bearer API key for both TTS and STT calls
Use Cases
Patterns agents use Cartesia 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 your Jentic One instance. 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
Jentic AI Readiness Score
This API is usable in Jentic One now. Its AI-readiness score against Jentic's framework shows where it stands today and where improvements would make it even easier for agents to use.
C
Cartesia API
- AI-Aware (A-)71/100
100
Foundational Compliance61
Developer Experience & Jentic Compatibility56
AI-Readiness & Agent Experience94
Agent Usability60
Security100
AI DiscoverabilityPowered by JenticScoring Framework 1.0.0 | Scoring Engine 0.4.0
Show dimension breakdown
100
Foundational Compliance
Base layer of spec validity and structural soundness.
Grade: A+Signals: 4
99%
Lint Results
Aggregated quality score from linter diagnostics, weighted by severity.
100%
Resolution Completeness
Percentage of `$ref` references that resolve successfully.
100%
Specification Validity
Checks whether the API description parses successfully and conforms to its declared specification (e.g., OpenAPI).
100%
Structural Integrity
Structural correctness score based on schema issues using logarithmic dampening.
61
Developer Experience & Jentic Compatibility
Clarity, completeness, and ingestion readiness for developers and tooling.
Grade: B-Signals: 4
0%
Example Density
How richly the API is illustrated with examples.
100%
Example Validity
Percentage of examples that conform to their schemas.
50%
Response Coverage
Percentage of operations with complete response definitions (success, client error, server error).
93%
Tooling Readiness
Health of API ingestion, bundling, and resolution within Jentic pipelines.
56
AI-Readiness & Agent Experience
Semantic breadth, depth, and agent comprehension for AI systems.
Grade: CSignals: 4
72%
Description Coverage
Coverage of descriptions across API elements.
0%
Error Standardization
Coverage of RFC 9457 Problem Details for error responses.
100%
OperationId Quality
Coverage, uniqueness, and casing consistency of operationIds for AI inference.
50%
Summary Coverage
Coverage of summaries across operations/tags/info.
94
Agent Usability
Functional utility, complexity comfort, and AI orchestration readiness.
Grade: A+Signals: 1
94%
Complexity Comfort
Agent comfort level based on API operational and structural complexity.
60
Security
Trust, risk posture, and security compliance.
Grade: B-Signals: 1
60%
Authentication Strength
Average quality of security schemes based on authentication method strength (weakest link for OAuth2).
100
AI Discoverability
Findability, semantic richness, and reasoning readiness.
Grade: A+Signals: 1
100%
Descriptive Richness
Clarity and depth of descriptions across API elements.
Score it yourself
Every API in the directory is allowlisted, so you can re-score it with no key required.
npx @jentic/api-scorecard-cli score <openapi-url>Why Jentic?
What agents get from Jentic-routed access to this vendor.
Setup
Wiring the Cartesia API by hand means passing your key as a bearer token on every call and handling the streaming byte and SSE responses from the Sonic text-to-speech routes on the api.cartesia.ai host yourself. Through Jentic you install once, import the Cartesia API from the API Directory, store the key once, and your agent calls it.
Permission scoping
Cartesia takes the text and audio in the request body, not the URL path, so you scope by operation: limit the agent to the ones it needs, such as synthesizing speech to bytes, and leave streaming SSE or transcription out of the allowed set until you want them.
Credential isolation
Your Cartesia API key is stored once, encrypted, by your own Jentic One instance and injected as the bearer token at execution time. It never enters the agent's prompt, logs, or context.
Intent-based discovery
Agents search Jentic by intent such as 'synthesize speech' or 'transcribe audio', and Jentic returns the matching Cartesia operation with its input schema so the agent calls the right TTS or STT endpoint without browsing the reference docs.
Related APIs
Alternatives and complements available in the Jentic catalogue.
FAQs
Specific to using Cartesia 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 with Jentic One, the self-hosted execution layer.
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 your Jentic One instance 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.
Can I limit what my agent is allowed to do with the Cartesia API?
Yes. Because Jentic One is self-hosted, your own rules decide which Cartesia operations the agent may call and which credentials it may use. Cartesia takes its text and audio in the request body rather than the URL path, so you scope by operation: allow only the ones the agent needs, such as synthesizing speech to bytes via /tts/bytes, and leave streaming SSE synthesis (/tts/sse) or file transcription (/stt) out of the allowed set. The Cartesia bearer key is injected only for the operations you permit, so the agent cannot reach endpoints you have not granted.
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