API reference | Llynx Speech API

The Llynx Speech API does two things: it turns spoken audio into text, and it turns text into spoken audio. A third endpoint tells you how much prepaid credit you have left for each.

Endpoint	Use it when
Generate speech (TTS)	You have text and need a natural voice reading it: assistant replies, notifications, IVR prompts, read-aloud.
Transcribe a recording (STT)	You have a short recording and need its words: voice notes, call snippets, voice commands, form dictation.
Read balances	You want to check remaining credit before sending work, or show usage to your own users.

Base URL and authentication

All requests go to https://api.llynx.io. Create an API key in your account and send it with every request as a bearer token:

Authorization: Bearer llp_live_…

The key is shown once when you create it. Keep it on your server; never ship it in a browser or mobile app. One key can call every endpoint.

Requests and responses

Transcription takes a multipart upload; speech generation takes JSON. Transcription answers with JSON and speech generation with a complete WAV file. Every response carries an X-Request-ID header; quote it when you contact us about a request.

Every request names its language with a tag from the Languages page. Errors come back as JSON with error.code, a readable message, the request_id and a retryable flag; the retries and failures page explains when to try again.

Credits

Each service draws on its own prepaid balance. Transcription is charged per second of audio and speech generation per character of input; see credits and packs for rates and packs. Successful responses report the credit reserved for the request in X-Llynx-Credits-Reserved.