Schemas

Every object the API sends, field by field. Times are ISO 8601 in UTC; durations and cue times are seconds.

Envelopes

JSON answers are wrapped the same way; the object is in payload. Signs (.sgn), videos and subtitle files come as files, unwrapped.

Success

{
  "success": true,
  "payload": { … },
  "timestamp": "2026-10-24T09:10:00.000Z"
}

Error

{
  "status": "error",
  "message": "That API key is not valid. Check it, or ask Signa for a new one.",
  "code": "INVALID_API_KEY",
  "details": { "code": "INVALID_API_KEY" },
  "timestamp": "2026-10-24T09:10:00.000Z"
}

Errors and limits lists the codes.

Account

GET /v1/api/me

Field	Type	Details
`organisation`	string	Your organisation's name.
`isTrial`	boolean	A trial: keys stop at expiresAt.
`expiresAt`	string \| null	When a trial ends.
`limits.monthlyChars`	integer \| null	Characters a month; null is no limit.
`limits.monthlyLiveMinutes`	integer \| null	Live minutes a month.
`limits.monthlyVideos`	integer \| null	Videos a month.
`thisMonth`	Usage	Below.

Usage, this calendar month (UTC):

Field	Type	Details
`requests`	integer	Calls made.
`chars`	integer	Characters signed.
`liveSeconds`	integer	Seconds connected to live sessions.
`videos`	integer	Videos made.
`subtitleSeconds`	integer	Seconds of audio turned into subtitles.

Client token

POST /v1/api/client-tokens

Field	Type	Details
`token`	string	`ct_…`: use it like the key, from a page or app.
`expiresAt`	string	When it stops working (at most an hour).

Languages

GET /v1/languages

Field	Type	Details
`spoken`	string[]	Codes you can send as `from` / `lang`.
`signed`	string[]	Codes you can send as `to`.

Signs (.sgn)

POST /v1/sign answers application/vnd.signa.sgn: one segment per word, each with its frame size, frame rate, word and frames of body, head and hand points. The byte layout is in The .sgn format.

Subtitles

POST /v1/subtitles with format=json

Field	Type	Details
`lang`	string	The spoken language.
`duration`	number	Seconds of audio in the file.
`text`	string	Everything said, as one string.
`cues`	Cue[]	In order.

Cue

Field	Type	Details
`start`	number	Seconds from the start of the file.
`end`	number	Seconds from the start of the file.
`text`	string	At most two lines (separated by \n) of 42 characters.

Speech

POST /v1/stt

Field	Type	Details
`text`	string	The transcript.
`lang`	string	The language it was heard in.
`provider`	string	Which recogniser answered.

POST /v1/tts

Field	Type	Details
`audio`	string	The speech, base64.
`provider`	string
`lang`	string

Overlay

POST /v1/overlays, GET /v1/overlays

Field	Type	Details
`id`	uuid	Use it in /v1/overlays/:id/… and in a live start message.
`orgId`	uuid	Your organisation.
`name`	string	Yours.
`captions`	boolean	Whether the caption line shows under the signer.
`createdAt`	string
`url`	string	Only when created: the page to put on screen, with its token after #.
`token`	string	Only when created: `ovt_…`, lets a screen watch the overlay.

POST /v1/overlays/:id/sign

Field	Type	Details
`words`	integer	Words signed onto the overlay.
`watchers`	integer	Screens showing the overlay when it was sent.

Live messages

From the server, as JSON text messages (and binary .sgn segments when signing).

type	Fields	When
`ready`	—	After the start message: send audio.
`speaking`	`active: boolean`	Speech started or stopped.
`partial`	`text`	What is heard so far, still changing.
`final`	`id, text`	Settled words, in order; ids only go up.
`signing`	`id`	With `sign: true`: that final's signs follow as binary messages.
`signed`	`id, words`	All of that final's signs were sent.
`sign_error`	`id, message`	That final could not be signed.
`error`	`message`	The session ended with a problem.
`done`	—	After a stop, everything was sent.

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