Cartesia
Cartesia builds real-time voice AI - the Sonic family of text-to-speech models, Ink speech-to-text models, and a Voice Agents platform for building and deploying telephone and web voice agents. The core generation surface is exposed both as REST (bytes and Server-Sent Events) and as a low-latency, bidirectional WebSocket protocol at wss://api.cartesia.ai for streaming TTS and STT with multiplexed contexts, word/phoneme timestamps, and mid-stream flush and cancel.
Real signal across most facets with visible, nameable gaps — the contract exists but is thin, or the portal is good while governance and commercial terms are absent.
API Evangelist profiles Cartesia the way a machine reads it — 30 machine-readable artifacts across 21 APIs, pulled from the provider's own public surface and indexed so a developer, an analyst, or an AI agent can evaluate it against every other provider on the network.
Every provider in the network is reduced to the same set of machine-readable artifacts — OpenAPI contracts, event specifications, GraphQL schemas, runnable collections, pricing and rate-limit signals, security posture, OAuth scopes, and the agent surfaces (MCP servers and skills) that let software drive the API on its own. We profile them because the interface is the part of a company you can actually inspect: it is a truer signal of what a provider does than any marketing page. From those artifacts we compute the Kin Score — Cartesia scores 48.6/100 (developing), with a separate agent-readiness read of 54/100 (agent ready). The full breakdown is below, followed by every artifact we hold — each card links through to its machine-readable definition on apis.io.
Kin Score
This is the API Evangelist rating — a single, repeatable read computed from the artifacts on this page. Green fill is points earned; the red track is points possible, so every bar shows earned-versus-possible at a glance.
Kin Score
How this is scored →scored 2026-07-27 · rubric v0.5
How we profile Cartesia
Each block below is one kind of artifact we hold for Cartesia. For each we say what it is and why it earns a place in the profile, then list every one we've indexed — capped at two rows, scroll within the panel for the rest.
APIs 21
Each API is captured as its own OpenAPI definition — every operation, parameter, and response. This is the single most useful machine-readable description of what an API does, and it's what lets us score, lint, mock, and generate against it without asking the provider for anything.
Individual APIs this provider publishes, each with its own machine-readable definition.
Cartesia TTS WebSocket API
Bidirectional, multiplexed WebSocket at wss://api.cartesia.ai/tts/websocket for realtime speech generation. Clients send JSON generation requests keyed by a context_id (continui...
Cartesia STT WebSocket API
Realtime transcription over WebSocket at wss://api.cartesia.ai/stt/websocket. Clients stream raw binary audio in 100ms chunks and issue finalize/close text commands; the server ...
Cartesia Agents API
Voice agent configuration and public templates.
Cartesia API Keys API
Standard API key metadata.
Cartesia Auth API
Short-lived, scoped access token generation.
Cartesia Calls API
Outbound call placement, batching, and history.
Cartesia Datasets API
Audio/text collections used to build custom fine-tunes and voices.
Cartesia Deployments API
Agent deployment inspection.
Cartesia Infill API
Generate audio that smoothly connects two existing audio segments.
Cartesia Knowledge Base API
Documents and folders used by agents.
Cartesia Metrics API
LLM-as-a-judge quality metrics for agents.
Cartesia Phone Numbers API
Telephony number provisioning and import.
Cartesia Pronunciation Dictionaries API
Custom pronunciation overrides referenced by TTS requests.
Cartesia Providers API
Linked telephony provider accounts.
Cartesia Speech-to-Text API
Batch transcription of an audio file of any length.
Cartesia Status API
API health and version.
Cartesia Text-to-Speech API
Single-shot and streamed speech generation over plain HTTP.
Cartesia Usage API
Credit and agent usage reporting.
Cartesia Voice Changer API
Transform speech into a different target voice.
Cartesia Voices API
Voice catalog management and voice cloning.
Cartesia Webhooks API
Webhook endpoint registration.
Scroll within the panel for all 21 ·
Open Collections 1
Open, tool-agnostic collections carry the same runnable value as Postman without locking you to one client — the portable, forkable form of the same exercise.
Open, tool-agnostic API collections (OpenAPI-derived and Bruno).
Cartesia API
OPEN COLLECTIONPricing Plans 1
Pricing is part of the interface. Machine-readable plans tell you what a tier costs and includes before you commit — one of the six things the Kin Score reads for commercial clarity.
Published pricing tiers and plan structures.
Rate Limits 1
Rate limits are the difference between a demo that works and a production integration that doesn't fall over. Publishing them is an operational-transparency signal — and a hard requirement for any agent that plans its own throughput.
Documented rate limits and quota policies.
Cartesia Ai Rate Limits
RATE LIMITSFinOps 1
Cost, billing, and metering signals let a buyer model the financial operations of an API before it's live. We profile them for the same reason we profile pricing: the money is part of the contract.
Cost, billing, and metering signals for API financial operations.
Cartesia Ai Finops
FINOPSEvent Specifications 1
Not every API is request/response. AsyncAPI describes the event-driven and streaming side — the webhooks and channels — so the asynchronous half of the interface is documented the same way the synchronous half is.
AsyncAPI definitions for this provider's event-driven and streaming APIs.
Cartesia Realtime WebSocket API (TTS + STT)
AsyncAPI 2.6 description of Cartesia's **documented public WebSocket API**. Unlike most providers in this catalog, Cartesia publishes a real, bidirectional WebSocket protocol - ...
ASYNCAPISpectral Rules 1
Governance rulesets we run against this provider's specs — the automated checks behind parts of the score. Profiling them makes the quality bar explicit and re-runnable, not a matter of opinion.
Cartesia API Rules
SPECTRALSecurity Posture 2
Authentication, domain security, vulnerability disclosure, and trust-center signals — the evidence that a provider takes security seriously enough to document it. We profile it because you can't govern what you can't see.
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Agentic Access 1
An x-agentic-access contract marks which operations are safe for an agent to run on its own and which need a human in the loop. It is the difference between an API an agent can use and one it can use safely.
Recommended x-agentic-access execution contracts for AI agents.
Resources
Every other property we hold for Cartesia — documentation, portals, status pages, policies, and corporate surface — grouped by the job it does, following the integrator's arc from getting started to running in production.
Documentation 1
Reference material describing how the API behaves
Agent Surfaces 1
MCP servers, agent skills, and machine-readable catalogs
Build 1
SDKs, sample code, and the tooling you integrate with
Access & Security 2
Authentication, authorization, and security posture
Operate 1
Status, limits, changes, and where to get help
Commercial 2
Pricing, plans, and the legal terms of use
Company 3
The organization behind the API
← All providers · Data indexed from github.com/api-evangelist/cartesia-ai · machine-readable index on apis.io