Layercode Realtime Voice WebSocket API

asyncapi: '2.6.0'
id: 'urn:com:layercode:agents:web:websocket'
info:
  title: Layercode Realtime Voice WebSocket API
  version: '1.0.0'
  description: |
    AsyncAPI 2.6 description of Layercode's **realtime voice transport**, a
    genuine bidirectional WebSocket documented at
    https://docs.layercode.com/api-reference/frontend-ws-api.

    Unlike one-way HTTP SSE, this is a true full-duplex WebSocket. The browser
    opens the connection at
    `wss://api.layercode.com/v1/agents/web/websocket?client_session_key=...`
    using a short-lived `client_session_key` obtained from the REST endpoint
    `POST /v1/agents/web/authorize_session` (modeled in
    `openapi/layercode-openapi.yml`).

    Over the socket the client streams base64-encoded 16-bit PCM microphone
    audio (8000 Hz, mono) to Layercode, and Layercode streams back synthesized
    speech (base64 16-bit PCM, 16000 Hz, mono), interim and final transcripts,
    streamed assistant text, and structured data, organized into user and
    assistant turns identified by `turn_id`.

    The companion webhook surface - where Layercode POSTs transcript events to
    your backend and your backend streams response.tts / response.data /
    response.end events back as Server-Sent Events - is documented at
    https://docs.layercode.com/api-reference/webhook-sse-api and summarized in
    `info.x-webhook-notes` below; it is a separate HTTP+SSE channel and is not
    modeled as WebSocket here.
  contact:
    name: API Evangelist
    email: kin@apievangelist.com
    url: https://apievangelist.com
  license:
    name: API documentation - Layercode Terms
    url: https://layercode.com/terms
  x-transport-notes:
    transport: WebSocket
    protocol: wss
    direction: bidirectional (full-duplex)
    url: 'wss://api.layercode.com/v1/agents/web/websocket'
    authorizedBy: 'client_session_key query parameter from POST /v1/agents/web/authorize_session'
    clientAudio: base64 16-bit PCM, 8000 Hz, mono
    serverAudio: base64 16-bit PCM, 16000 Hz, mono
    source: https://docs.layercode.com/api-reference/frontend-ws-api
  x-webhook-notes:
    transport: HTTP Server-Sent Events (SSE)
    direction: 'Layercode POSTs JSON events to your backend webhook; backend streams SSE back'
    requestEvents: [session.start, message, data, session.update, session.end]
    responseEvents: [response.tts, response.data, response.end, response.hangup]
    signatureHeader: layercode-signature
    source: https://docs.layercode.com/api-reference/webhook-sse-api
defaultContentType: application/json
servers:
  layercode:
    url: api.layercode.com/v1/agents/web/websocket
    protocol: wss
    description: |
      Layercode realtime voice WebSocket. The browser connects with a
      short-lived client_session_key query parameter. The connection is
      full-duplex: the client publishes microphone audio and control messages,
      and the server publishes audio, transcripts, text, and data events.
channels:
  /v1/agents/web/websocket:
    description: |
      Realtime voice channel. Opened by the browser with
      `?client_session_key=...`. Both directions exchange JSON text frames; all
      audio payloads are carried as base64 strings inside JSON messages.
    bindings:
      ws:
        query:
          type: object
          properties:
            client_session_key:
              type: string
              description: Short-lived session key from authorize_session.
          required:
            - client_session_key
    publish:
      operationId: clientToServer
      summary: Messages the client sends to Layercode.
      message:
        oneOf:
          - $ref: '#/components/messages/ClientReady'
          - $ref: '#/components/messages/ClientAudio'
          - $ref: '#/components/messages/TriggerTurnStart'
          - $ref: '#/components/messages/TriggerTurnEnd'
          - $ref: '#/components/messages/TriggerAudioReplayFinished'
          - $ref: '#/components/messages/ClientResponseText'
          - $ref: '#/components/messages/ClientResponseData'
    subscribe:
      operationId: serverToClient
      summary: Messages Layercode sends to the client.
      message:
        oneOf:
          - $ref: '#/components/messages/TurnStart'
          - $ref: '#/components/messages/ResponseAudio'
          - $ref: '#/components/messages/ResponseTextDelta'
          - $ref: '#/components/messages/ResponseText'
          - $ref: '#/components/messages/UserTranscriptInterimDelta'
          - $ref: '#/components/messages/UserTranscriptDelta'
          - $ref: '#/components/messages/UserTranscript'
          - $ref: '#/components/messages/ResponseData'
components:
  messages:
    ClientReady:
      name: client.ready
      title: Client ready
      summary: Signals the client is connected and ready to stream.
      payload:
        type: object
        properties:
          type:
            type: string
            const: client.ready
    ClientAudio:
      name: client.audio
      title: Client audio chunk
      summary: A chunk of microphone audio from the browser.
      payload:
        type: object
        properties:
          type:
            type: string
            const: client.audio
          content:
            type: string
            description: Base64-encoded 16-bit PCM audio, 8000 Hz, mono.
    TriggerTurnStart:
      name: trigger.turn.start
      title: Turn start trigger (push-to-talk)
      payload:
        type: object
        properties:
          type:
            type: string
            const: trigger.turn.start
          role:
            type: string
            const: user
    TriggerTurnEnd:
      name: trigger.turn.end
      title: Turn end trigger (push-to-talk)
      payload:
        type: object
        properties:
          type:
            type: string
            const: trigger.turn.end
          role:
            type: string
            const: user
    TriggerAudioReplayFinished:
      name: trigger.response.audio.replay_finished
      title: Audio replay finished
      summary: Client finished playing back a response audio turn.
      payload:
        type: object
        properties:
          type:
            type: string
            const: trigger.response.audio.replay_finished
          reason:
            type: string
          turn_id:
            type: string
            format: uuid
    ClientResponseText:
      name: client.response.text
      title: Client text message
      summary: A typed text message from the user.
      payload:
        type: object
        properties:
          type:
            type: string
            const: client.response.text
          content:
            type: string
    ClientResponseData:
      name: client.response.data
      title: Client structured data
      summary: Arbitrary structured JSON emitted by the client UI.
      payload:
        type: object
        properties:
          type:
            type: string
            const: client.response.data
          data:
            type: object
            additionalProperties: true
    TurnStart:
      name: turn.start
      title: Turn start
      payload:
        type: object
        properties:
          type:
            type: string
            const: turn.start
          role:
            type: string
            enum:
              - user
              - assistant
          turn_id:
            type: string
            format: uuid
    ResponseAudio:
      name: response.audio
      title: Response audio chunk
      summary: Synthesized speech audio from Layercode.
      payload:
        type: object
        properties:
          type:
            type: string
            const: response.audio
          content:
            type: string
            description: Base64-encoded 16-bit PCM audio, 16000 Hz, mono.
          delta_id:
            type: string
            format: uuid
          turn_id:
            type: string
            format: uuid
    ResponseTextDelta:
      name: response.text.delta
      title: Response text delta
      payload:
        type: object
        properties:
          type:
            type: string
            const: response.text.delta
          content:
            type: string
          turn_id:
            type: string
            format: uuid
    ResponseText:
      name: response.text
      title: Response text (complete)
      payload:
        type: object
        properties:
          type:
            type: string
            const: response.text
          content:
            type: string
          turn_id:
            type: string
            format: uuid
    UserTranscriptInterimDelta:
      name: user.transcript.interim_delta
      title: Interim transcript delta
      payload:
        type: object
        properties:
          type:
            type: string
            const: user.transcript.interim_delta
          content:
            type: string
          turn_id:
            type: string
            format: uuid
    UserTranscriptDelta:
      name: user.transcript.delta
      title: Final transcript delta
      payload:
        type: object
        properties:
          type:
            type: string
            const: user.transcript.delta
          content:
            type: string
          turn_id:
            type: string
            format: uuid
    UserTranscript:
      name: user.transcript
      title: Complete turn transcript
      payload:
        type: object
        properties:
          type:
            type: string
            const: user.transcript
          content:
            type: string
          turn_id:
            type: string
            format: uuid
    ResponseData:
      name: response.data
      title: Response structured data
      summary: Structured JSON pushed to the client without audio.
      payload:
        type: object
        properties:
          type:
            type: string
            const: response.data
          content:
            type: object
            additionalProperties: true
          turn_id:
            type: string
            format: uuid