> ## Documentation Index > Fetch the complete documentation index at: https://heygen-1fa696a7.mintlify.app/llms.txt > Use this file to discover all available pages before exploring further. # Generate Speech > Synthesize speech audio from text using a specified voice. The voice must support the starfish engine — use GET /v3/voices?engine=starfish to find compatible voices. Supports plain text and SSML. Speed range: 0.5–2.0x. Returns a URL to the generated audio file along with duration and optional word-level timestamps. ## OpenAPI ````yaml /openapi/external-api.json post /v3/voices/speech openapi: 3.1.0 info: title: HeyGen External API version: 1.0.0 description: >- HeyGen's external API for programmatic AI video creation. See https://docs.heygen.com for full documentation. contact: name: HeyGen Product Infra url: https://heygen.com servers: - url: https://api.heygen.com description: Production security: - ApiKeyAuth: [] - BearerAuth: [] tags: - name: Video Agent description: Create videos from text prompts using AI - name: Videos description: Create, list, retrieve, and delete videos - name: Voices description: Text-to-speech and voice management - name: Audio description: Search the background-music and sound-effects catalog - name: Video Translate description: Translate videos into other languages - name: User description: Account information and billing - name: Avatars description: List and manage avatars and looks - name: Assets description: Upload files for use in video creation - name: Webhooks description: Manage webhook endpoints and events - name: Lipsync description: Dub or replace audio on existing videos - name: Brand description: >- Brand-related resources — brand kits (colors, fonts, logos) and brand glossaries (custom term translations) paths: /v3/voices/speech: post: tags: - Voices summary: Generate Speech description: >- Synthesize speech audio from text using a specified voice. The voice must support the starfish engine — use GET /v3/voices?engine=starfish to find compatible voices. Supports plain text and SSML. Speed range: 0.5–2.0x. Returns a URL to the generated audio file along with duration and optional word-level timestamps. operationId: createSpeechV3 requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/TextToSpeechRequest' responses: '200': description: Successful response content: application/json: schema: type: object properties: data: $ref: '#/components/schemas/TextToSpeechResponseData' '400': description: Invalid request parameters content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: invalid_parameter message: '''voice_id'' is required.' param: voice_id doc_url: null '401': description: Authentication failed content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: authentication_failed message: Invalid or expired API key. Verify your x-api-key header. param: null doc_url: null '429': description: Rate limit exceeded content: application/json: schema: type: object properties: error: $ref: '#/components/schemas/StandardAPIError' example: error: code: rate_limit_exceeded message: >- Too many requests. Retry after the duration specified in the Retry-After header. param: null doc_url: null headers: Retry-After: description: Seconds to wait before retrying schema: type: integer security: - ApiKeyAuth: [] - BearerAuth: [] components: schemas: TextToSpeechRequest: additionalProperties: false description: Request body for text-to-speech generation. properties: text: description: Text to synthesize (1-5000 characters). maxLength: 5000 minLength: 1 title: Text type: string voice_id: description: >- Voice ID to use. The voice must support the starfish engine. Filter compatible voices by passing engine=starfish to the voice listing endpoint. title: Voice Id type: string input_type: default: text description: >- Type of the input: 'text' for plain text, 'ssml' for SSML markup. Defaults to 'text'. title: Input Type type: string speed: default: 1 description: Speed multiplier (0.5-2.0). maximum: 2 minimum: 0.5 title: Speed type: number language: anyOf: - type: string - type: 'null' default: null description: >- Base language code (e.g. 'en', 'pt', 'zh'). Optional — auto-detected from text when omitted. title: Language locale: anyOf: - type: string - type: 'null' default: null description: >- BCP-47 locale tag (e.g. 'en-US', 'pt-BR'). When set, language is inferred from locale. title: Locale required: - text - voice_id title: TextToSpeechRequest type: object TextToSpeechResponseData: description: Response payload for text-to-speech generation. properties: audio_url: description: URL of the generated audio file. examples: - https://files.heygen.ai/audio/tts_abc123.mp3 title: Audio Url type: string duration: description: Duration of the audio in seconds. examples: - 4.5 title: Duration type: number request_id: anyOf: - type: string - type: 'null' default: null description: Unique identifier for this generation request. examples: - req_abc123 title: Request Id word_timestamps: anyOf: - items: $ref: '#/components/schemas/WordWithTimestamp' type: array - type: 'null' default: null description: Word-level timing data. title: Word Timestamps required: - audio_url - duration title: TextToSpeechResponseData type: object StandardAPIError: type: object properties: code: type: string description: Machine-readable error code example: invalid_parameter message: type: string description: Human-readable error message example: Video not found param: type: - string - 'null' description: Which request field caused the error doc_url: type: - string - 'null' description: Link to error documentation required: - code - message WordWithTimestamp: description: Word-level timing data from TTS generation. properties: word: description: The word. examples: - Hello title: Word type: string start: description: Start time in seconds. examples: - 0 title: Start type: number end: description: End time in seconds. examples: - 0.35 title: End type: number required: - word - start - end title: WordWithTimestamp type: object securitySchemes: ApiKeyAuth: type: apiKey in: header name: x-api-key description: HeyGen API key. Obtain from your HeyGen dashboard. BearerAuth: type: http scheme: bearer description: OAuth2 bearer token. ````