> ## Documentation Index > Fetch the complete documentation index at: https://docs.phone.wixzel.com/llms.txt > Use this file to discover all available pages before exploring further. # List an engine's languages > Which languages an engine can hold a conversation in. A composed engine lists a language only when both its speech-to-text and its text-to-speech serve it — one that is transcribed but cannot be spoken back is not a language the engine supports end to end. Use a `code` from here as the agent's `language`, or as `voice.stt.language` / `voice.realtime.language`. Unknown engine ids are a 404; an engine whose provider is momentarily degraded still answers, with `available: false`. ## OpenAPI ````yaml /openapi.json get /v1/engines/{engine}/languages openapi: 3.1.0 info: title: Wixzel Phone API version: '2026-09-01' description: >- APIs for AI voice agents. One key, one balance, every voice engine. ## Authentication Send your key as `Authorization: Bearer wv_live_...`. Keys are scoped — grant only what an integration needs. There is no admin scope. ## Versioning The `/v1` prefix covers additive changes. Behavioural changes ship behind a dated `Wixzel-Version` header, and existing keys keep the behaviour they were created with. ## Money Amounts are integer **micro-USD** (1,000,000 = $1.00). Voice usage is billed per second, per token and per character, so a float dollar figure cannot represent it without disagreeing with the ledger. ## Errors Every error carries a stable `code` and a `request_id`. Match on `code`; the `message` is for humans and may change. contact: name: Wixzel Phone url: https://phone.wixzel.com servers: - url: https://api.phone.wixzel.com description: Production security: [] tags: - name: Calls description: Place calls and read what happened on them. - name: Agents description: The prompt, voice and behaviour of a caller. - name: Leads description: People to call, and data to merge into prompts. - name: Campaigns description: Call a list of leads with one agent. - name: Knowledge bases description: Facts an agent can draw on mid-call. - name: Phone numbers description: Numbers on your SIP trunks. - name: SIP trunks description: Your carrier connections. - name: Appointments description: Bookings, including ones agents make on calls. - name: Usage description: Itemised billing lines. - name: Billing description: Balance, ledger and top-ups. - name: API keys description: Create, scope and rotate keys. - name: Engines description: What the platform can serve, and what it costs. paths: /v1/engines/{engine}/languages: get: tags: - Engines summary: List an engine's languages description: >- Which languages an engine can hold a conversation in. A composed engine lists a language only when both its speech-to-text and its text-to-speech serve it — one that is transcribed but cannot be spoken back is not a language the engine supports end to end. Use a `code` from here as the agent's `language`, or as `voice.stt.language` / `voice.realtime.language`. Unknown engine ids are a 404; an engine whose provider is momentarily degraded still answers, with `available: false`. parameters: - schema: type: string example: classic required: true name: engine in: path responses: '200': description: Supported languages content: application/json: schema: $ref: '#/components/schemas/EngineLanguageList' '400': description: Invalid request content: application/json: schema: $ref: '#/components/schemas/Error' '401': description: Missing or invalid API key content: application/json: schema: $ref: '#/components/schemas/Error' '403': description: Key lacks the required scope content: application/json: schema: $ref: '#/components/schemas/Error' '404': description: No such record content: application/json: schema: $ref: '#/components/schemas/Error' '429': description: Rate limited. Retry after the interval in `Retry-After`. content: application/json: schema: $ref: '#/components/schemas/Error' security: - bearerAuth: [] components: schemas: EngineLanguageList: type: object properties: object: type: string enum: - list engine: type: string example: sarvam available: type: boolean description: >- Whether the engine can carry a call right now. The language list is returned either way, so a picker still renders during a provider outage. data: type: array items: $ref: '#/components/schemas/EngineLanguage' required: - object - engine - available - data Error: type: object properties: error: type: object properties: type: type: string enum: - invalid_request_error - authentication_error - permission_error - rate_limit_error - insufficient_credits - not_found_error - conflict_error - api_error code: type: string description: Stable machine-readable code. example: agent_not_found message: type: string description: >- Human-readable explanation. Do not match on this — match on code. param: type: string description: Which field caused the failure, when applicable. doc_url: type: string request_id: type: string description: Quote this when asking for help. example: req_01HXYZ... required: - type - code - message - request_id required: - error EngineLanguage: type: object properties: code: type: string description: >- The value to send as `voice.stt.language`, `voice.realtime.language` or the agent's `language`. Regional variants of a listed code are accepted and resolve to the same pipeline, so `en-GB` works wherever `en` is listed. example: ta-IN name: type: string description: English name of the language. example: Tamil components: type: array items: type: string enum: - stt - tts - realtime description: >- Which stages of this engine serve the language. A composed engine lists a language only when both its speech-to-text and its text-to-speech support it. required: - code - name - components securitySchemes: bearerAuth: type: http scheme: bearer description: >- Your Wixzel Phone API key: `Authorization: Bearer wv_live_...`. Keys are scoped; grant only what the integration needs. ````