Voices

openapi: 3.0.1
info:
  title: Retell AI API
  description: >-
    REST API for building, testing, and deploying AI voice agents that make and
    receive phone and web calls. Configure a response engine (Retell LLM, a
    custom LLM, or a Conversation Flow), attach a voice, provision phone numbers,
    place outbound and web calls, run batch campaigns, ground agents with
    knowledge bases, and read back transcripts, recordings, and call analysis.
    All endpoints are authenticated with a Bearer API key.
  termsOfService: https://www.retellai.com/terms-of-service
  contact:
    name: Retell AI Support
    url: https://docs.retellai.com
  version: '2.0'
servers:
  - url: https://api.retellai.com
security:
  - api_key: []
tags:
  - name: Agent
  - name: Retell LLM
  - name: Conversation Flow
  - name: Phone Call
  - name: Web Call
  - name: Call
  - name: Phone Number
  - name: Voice
  - name: Knowledge Base
  - name: Batch Call
  - name: Concurrency
paths:
  /create-agent:
    post:
      operationId: createAgent
      tags:
        - Agent
      summary: Create a new voice agent.
      description: >-
        Creates an agent that pairs a response engine (retell-llm, custom-llm, or
        conversation-flow) with a voice and call-behavior settings.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/AgentRequest'
      responses:
        '201':
          description: Agent created.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/AgentResponse'
  /get-agent/{agent_id}:
    get:
      operationId: getAgent
      tags:
        - Agent
      summary: Retrieve an agent.
      parameters:
        - $ref: '#/components/parameters/AgentId'
        - $ref: '#/components/parameters/Version'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/AgentResponse'
  /list-agents:
    get:
      operationId: listAgents
      tags:
        - Agent
      summary: List all agents.
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/AgentResponse'
  /update-agent/{agent_id}:
    patch:
      operationId: updateAgent
      tags:
        - Agent
      summary: Update an agent.
      parameters:
        - $ref: '#/components/parameters/AgentId'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/AgentRequest'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/AgentResponse'
  /delete-agent/{agent_id}:
    delete:
      operationId: deleteAgent
      tags:
        - Agent
      summary: Delete an agent.
      parameters:
        - $ref: '#/components/parameters/AgentId'
      responses:
        '204':
          description: Agent deleted.
  /create-retell-llm:
    post:
      operationId: createRetellLLM
      tags:
        - Retell LLM
      summary: Create a Retell LLM response engine.
      description: >-
        Creates a Retell-managed LLM response engine (prompt, model, tools,
        states, and knowledge base references) that an agent can use to drive the
        conversation.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/RetellLLMRequest'
      responses:
        '201':
          description: Retell LLM created.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/RetellLLMResponse'
  /get-retell-llm/{llm_id}:
    get:
      operationId: getRetellLLM
      tags:
        - Retell LLM
      summary: Retrieve a Retell LLM.
      parameters:
        - $ref: '#/components/parameters/LlmId'
        - $ref: '#/components/parameters/Version'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/RetellLLMResponse'
  /list-retell-llms:
    get:
      operationId: listRetellLLMs
      tags:
        - Retell LLM
      summary: List all Retell LLMs.
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/RetellLLMResponse'
  /update-retell-llm/{llm_id}:
    patch:
      operationId: updateRetellLLM
      tags:
        - Retell LLM
      summary: Update a Retell LLM.
      parameters:
        - $ref: '#/components/parameters/LlmId'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/RetellLLMRequest'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/RetellLLMResponse'
  /delete-retell-llm/{llm_id}:
    delete:
      operationId: deleteRetellLLM
      tags:
        - Retell LLM
      summary: Delete a Retell LLM.
      parameters:
        - $ref: '#/components/parameters/LlmId'
      responses:
        '204':
          description: Retell LLM deleted.
  /create-conversation-flow:
    post:
      operationId: createConversationFlow
      tags:
        - Conversation Flow
      summary: Create a conversation flow.
      description: >-
        Creates a node/edge conversation flow response engine for visually
        structured, deterministic agent conversations.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ConversationFlowRequest'
      responses:
        '201':
          description: Conversation flow created.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ConversationFlowResponse'
  /get-conversation-flow/{conversation_flow_id}:
    get:
      operationId: getConversationFlow
      tags:
        - Conversation Flow
      summary: Retrieve a conversation flow.
      parameters:
        - $ref: '#/components/parameters/ConversationFlowId'
        - $ref: '#/components/parameters/Version'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ConversationFlowResponse'
  /list-conversation-flows:
    get:
      operationId: listConversationFlows
      tags:
        - Conversation Flow
      summary: List all conversation flows.
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/ConversationFlowResponse'
  /update-conversation-flow/{conversation_flow_id}:
    patch:
      operationId: updateConversationFlow
      tags:
        - Conversation Flow
      summary: Update a conversation flow.
      parameters:
        - $ref: '#/components/parameters/ConversationFlowId'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ConversationFlowRequest'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ConversationFlowResponse'
  /delete-conversation-flow/{conversation_flow_id}:
    delete:
      operationId: deleteConversationFlow
      tags:
        - Conversation Flow
      summary: Delete a conversation flow.
      parameters:
        - $ref: '#/components/parameters/ConversationFlowId'
      responses:
        '204':
          description: Conversation flow deleted.
  /v2/create-phone-call:
    post:
      operationId: createPhoneCall
      tags:
        - Phone Call
      summary: Create an outbound phone call.
      description: >-
        Places an outbound PSTN call from a number you own to a destination
        number, handled by the agent bound to the from_number (or an override
        agent).
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreatePhoneCallRequest'
      responses:
        '201':
          description: Phone call registered.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PhoneCallResponse'
  /v2/create-web-call:
    post:
      operationId: createWebCall
      tags:
        - Web Call
      summary: Create a web call.
      description: >-
        Registers a browser-based (WebRTC) call and returns an access_token to
        hand to the Retell Web Client SDK in your frontend.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateWebCallRequest'
      responses:
        '201':
          description: Web call registered.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/WebCallResponse'
  /get-call/{call_id}:
    get:
      operationId: getCall
      tags:
        - Call
      summary: Retrieve a call.
      description: >-
        Returns the full call object including status, transcript, recording URL,
        call analysis, and cost breakdown.
      parameters:
        - name: call_id
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Call'
  /list-calls:
    post:
      operationId: listCalls
      tags:
        - Call
      summary: List calls.
      description: >-
        Lists calls with optional filter criteria (agent, status, direction,
        timestamp ranges), sort order, and pagination.
      requestBody:
        required: false
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ListCallsRequest'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Call'
  /create-batch-call:
    post:
      operationId: createBatchCall
      tags:
        - Batch Call
      summary: Create a batch call.
      description: >-
        Queues an outbound calling campaign to many recipients from a single
        from_number, subject to available concurrency.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateBatchCallRequest'
      responses:
        '201':
          description: Batch call created.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/BatchCallResponse'
  /create-phone-number:
    post:
      operationId: createPhoneNumber
      tags:
        - Phone Number
      summary: Buy a phone number.
      description: >-
        Provisions (purchases) a new phone number and optionally binds inbound
        and outbound agents to it.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreatePhoneNumberRequest'
      responses:
        '201':
          description: Phone number provisioned.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PhoneNumberResponse'
  /import-phone-number:
    post:
      operationId: importPhoneNumber
      tags:
        - Phone Number
      summary: Import an existing phone number.
      description: >-
        Connects a number you already own via your own SIP trunk / elastic SIP
        trunking for use with Retell agents.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ImportPhoneNumberRequest'
      responses:
        '201':
          description: Phone number imported.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PhoneNumberResponse'
  /get-phone-number/{phone_number}:
    get:
      operationId: getPhoneNumber
      tags:
        - Phone Number
      summary: Retrieve a phone number.
      parameters:
        - $ref: '#/components/parameters/PhoneNumber'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PhoneNumberResponse'
  /list-phone-numbers:
    get:
      operationId: listPhoneNumbers
      tags:
        - Phone Number
      summary: List phone numbers.
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/PhoneNumberResponse'
  /update-phone-number/{phone_number}:
    patch:
      operationId: updatePhoneNumber
      tags:
        - Phone Number
      summary: Update a phone number.
      parameters:
        - $ref: '#/components/parameters/PhoneNumber'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/UpdatePhoneNumberRequest'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PhoneNumberResponse'
  /delete-phone-number/{phone_number}:
    delete:
      operationId: deletePhoneNumber
      tags:
        - Phone Number
      summary: Delete (release) a phone number.
      parameters:
        - $ref: '#/components/parameters/PhoneNumber'
      responses:
        '204':
          description: Phone number released.
  /list-voices:
    get:
      operationId: listVoices
      tags:
        - Voice
      summary: List all available voices.
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Voice'
  /get-voice/{voice_id}:
    get:
      operationId: getVoice
      tags:
        - Voice
      summary: Retrieve a voice.
      parameters:
        - name: voice_id
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Voice'
  /create-knowledge-base:
    post:
      operationId: createKnowledgeBase
      tags:
        - Knowledge Base
      summary: Create a knowledge base.
      description: >-
        Creates a knowledge base from texts, files, and/or URLs that agents can
        retrieve from (RAG) during calls.
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              $ref: '#/components/schemas/CreateKnowledgeBaseRequest'
      responses:
        '201':
          description: Knowledge base created.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/KnowledgeBaseResponse'
  /get-knowledge-base/{knowledge_base_id}:
    get:
      operationId: getKnowledgeBase
      tags:
        - Knowledge Base
      summary: Retrieve a knowledge base.
      parameters:
        - $ref: '#/components/parameters/KnowledgeBaseId'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/KnowledgeBaseResponse'
  /list-knowledge-bases:
    get:
      operationId: listKnowledgeBases
      tags:
        - Knowledge Base
      summary: List all knowledge bases.
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/KnowledgeBaseResponse'
  /delete-knowledge-base/{knowledge_base_id}:
    delete:
      operationId: deleteKnowledgeBase
      tags:
        - Knowledge Base
      summary: Delete a knowledge base.
      parameters:
        - $ref: '#/components/parameters/KnowledgeBaseId'
      responses:
        '204':
          description: Knowledge base deleted.
  /add-knowledge-base-sources/{knowledge_base_id}:
    post:
      operationId: addKnowledgeBaseSources
      tags:
        - Knowledge Base
      summary: Add sources to a knowledge base.
      parameters:
        - $ref: '#/components/parameters/KnowledgeBaseId'
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              $ref: '#/components/schemas/AddKnowledgeBaseSourcesRequest'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/KnowledgeBaseResponse'
  /delete-knowledge-base-source/{knowledge_base_id}/source/{source_id}:
    delete:
      operationId: deleteKnowledgeBaseSource
      tags:
        - Knowledge Base
      summary: Delete a knowledge base source.
      parameters:
        - $ref: '#/components/parameters/KnowledgeBaseId'
        - name: source_id
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/KnowledgeBaseResponse'
  /get-concurrency:
    get:
      operationId: getConcurrency
      tags:
        - Concurrency
      summary: Get current and maximum call concurrency.
      description: >-
        Returns the organization's current number of ongoing calls, base and
        purchased concurrency limits, burst settings, and reserved inbound
        concurrency.
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ConcurrencyResponse'
components:
  securitySchemes:
    api_key:
      type: http
      scheme: bearer
      bearerFormat: apiKey
      description: 'Retell API key, sent as: Authorization: Bearer <RETELL_API_KEY>'
  parameters:
    AgentId:
      name: agent_id
      in: path
      required: true
      schema:
        type: string
    LlmId:
      name: llm_id
      in: path
      required: true
      schema:
        type: string
    ConversationFlowId:
      name: conversation_flow_id
      in: path
      required: true
      schema:
        type: string
    KnowledgeBaseId:
      name: knowledge_base_id
      in: path
      required: true
      schema:
        type: string
    PhoneNumber:
      name: phone_number
      in: path
      required: true
      description: Phone number in E.164 format.
      schema:
        type: string
    Version:
      name: version
      in: query
      required: false
      description: Specific version (integer) or version tag to retrieve.
      schema:
        type: string
  schemas:
    ResponseEngine:
      type: object
      description: The engine that produces agent responses during a call.
      required:
        - type
      properties:
        type:
          type: string
          enum:
            - retell-llm
            - custom-llm
            - conversation-flow
        llm_id:
          type: string
          description: Retell LLM id when type is retell-llm.
        llm_websocket_url:
          type: string
          description: >-
            Your WebSocket URL when type is custom-llm. Retell connects to
            `{this-url}/{call_id}` at call start.
        conversation_flow_id:
          type: string
          description: Conversation flow id when type is conversation-flow.
        version:
          type: integer
    AgentRequest:
      type: object
      required:
        - response_engine
        - voice_id
      properties:
        response_engine:
          $ref: '#/components/schemas/ResponseEngine'
        voice_id:
          type: string
          example: 11labs-Adrian
        agent_name:
          type: string
        voice_model:
          type: string
        voice_speed:
          type: number
          minimum: 0.5
          maximum: 2
        voice_temperature:
          type: number
          minimum: 0
          maximum: 2
        language:
          type: string
          default: en-US
        webhook_url:
          type: string
        responsiveness:
          type: number
          minimum: 0
          maximum: 1
        interruption_sensitivity:
          type: number
          minimum: 0
          maximum: 1
        ambient_sound:
          type: string
        end_call_after_silence_ms:
          type: integer
        stt_mode:
          type: string
          enum:
            - fast
            - accurate
    AgentResponse:
      allOf:
        - $ref: '#/components/schemas/AgentRequest'
        - type: object
          properties:
            agent_id:
              type: string
            version:
              type: integer
            is_published:
              type: boolean
            last_modification_timestamp:
              type: integer
    RetellLLMRequest:
      type: object
      properties:
        general_prompt:
          type: string
          description: General prompt appended to the system prompt in every state.
        model:
          type: string
          default: gpt-4.1
        model_temperature:
          type: number
          minimum: 0
          maximum: 1
        s2s_model:
          type: string
        begin_message:
          type: string
          description: First utterance said by the agent.
        start_speaker:
          type: string
          enum:
            - agent
            - user
        general_tools:
          type: array
          items:
            $ref: '#/components/schemas/Tool'
        states:
          type: array
          items:
            type: object
        starting_state:
          type: string
        knowledge_base_ids:
          type: array
          items:
            type: string
        default_dynamic_variables:
          type: object
          additionalProperties:
            type: string
    RetellLLMResponse:
      allOf:
        - $ref: '#/components/schemas/RetellLLMRequest'
        - type: object
          properties:
            llm_id:
              type: string
            version:
              type: integer
            is_published:
              type: boolean
            last_modification_timestamp:
              type: integer
    Tool:
      type: object
      properties:
        type:
          type: string
          enum:
            - end_call
            - transfer_call
            - check_availability_cal
            - book_appointment_cal
            - press_digit
            - custom
        name:
          type: string
        description:
          type: string
        url:
          type: string
          description: Webhook URL for a custom tool.
    ConversationFlowRequest:
      type: object
      properties:
        global_prompt:
          type: string
        nodes:
          type: array
          description: Flow nodes (conversation, function, transfer, end, etc.).
          items:
            type: object
        start_node_id:
          type: string
        model:
          type: string
        knowledge_base_ids:
          type: array
          items:
            type: string
    ConversationFlowResponse:
      allOf:
        - $ref: '#/components/schemas/ConversationFlowRequest'
        - type: object
          properties:
            conversation_flow_id:
              type: string
            version:
              type: integer
            is_published:
              type: boolean
    CreatePhoneCallRequest:
      type: object
      required:
        - from_number
        - to_number
      properties:
        from_number:
          type: string
          description: E.164 number you own.
          example: '+14157774444'
        to_number:
          type: string
          description: E.164 destination number.
          example: '+12137774445'
        override_agent_id:
          type: string
        override_agent_version:
          type: integer
        metadata:
          type: object
        retell_llm_dynamic_variables:
          type: object
          additionalProperties:
            type: string
        custom_sip_headers:
          type: object
          additionalProperties:
            type: string
    PhoneCallResponse:
      type: object
      properties:
        call_id:
          type: string
        call_type:
          type: string
          enum:
            - phone_call
        agent_id:
          type: string
        agent_version:
          type: integer
        call_status:
          $ref: '#/components/schemas/CallStatus'
        from_number:
          type: string
        to_number:
          type: string
        direction:
          type: string
          enum:
            - inbound
            - outbound
        telephony_identifier:
          type: object
    CreateWebCallRequest:
      type: object
      required:
        - agent_id
      properties:
        agent_id:
          type: string
        agent_version:
          type: integer
        metadata:
          type: object
        retell_llm_dynamic_variables:
          type: object
          additionalProperties:
            type: string
    WebCallResponse:
      type: object
      properties:
        call_id:
          type: string
        call_type:
          type: string
          enum:
            - web_call
        access_token:
          type: string
          description: Token to pass to the Retell Web Client SDK in your frontend.
        agent_id:
          type: string
        agent_version:
          type: integer
        call_status:
          $ref: '#/components/schemas/CallStatus'
    ListCallsRequest:
      type: object
      properties:
        filter_criteria:
          type: object
          properties:
            agent_id:
              type: array
              items:
                type: string
            call_status:
              type: array
              items:
                $ref: '#/components/schemas/CallStatus'
            direction:
              type: array
              items:
                type: string
        sort_order:
          type: string
          enum:
            - ascending
            - descending
        limit:
          type: integer
        pagination_key:
          type: string
    CallStatus:
      type: string
      enum:
        - registered
        - ongoing
        - ended
        - error
    Call:
      type: object
      properties:
        call_id:
          type: string
        call_type:
          type: string
          enum:
            - phone_call
            - web_call
        agent_id:
          type: string
        call_status:
          $ref: '#/components/schemas/CallStatus'
        from_number:
          type: string
        to_number:
          type: string
        direction:
          type: string
        start_timestamp:
          type: integer
        end_timestamp:
          type: integer
        duration_ms:
          type: integer
        transcript:
          type: string
        transcript_object:
          type: array
          items:
            type: object
        recording_url:
          type: string
        public_log_url:
          type: string
        disconnection_reason:
          type: string
        call_analysis:
          $ref: '#/components/schemas/CallAnalysis'
        call_cost:
          $ref: '#/components/schemas/CallCost'
        metadata:
          type: object
    CallAnalysis:
      type: object
      properties:
        call_summary:
          type: string
        user_sentiment:
          type: string
          enum:
            - Negative
            - Positive
            - Neutral
            - Unknown
        call_successful:
          type: boolean
        in_voicemail:
          type: boolean
        custom_analysis_data:
          type: object
    CallCost:
      type: object
      properties:
        combined_cost:
          type: number
          description: Total cost of the call in cents.
        total_duration_seconds:
          type: integer
        product_costs:
          type: array
          items:
            type: object
            properties:
              product:
                type: string
                description: e.g. retell_platform, tts, llm, telephony.
              unit_price:
                type: number
              cost:
                type: number
    CreateBatchCallRequest:
      type: object
      required:
        - from_number
        - tasks
      properties:
        from_number:
          type: string
        name:
          type: string
        trigger_timestamp:
          type: integer
          description: Unix ms at which to start the campaign; omit to start immediately.
        tasks:
          type: array
          items:
            type: object
            required:
              - to_number
            properties:
              to_number:
                type: string
              retell_llm_dynamic_variables:
                type: object
                additionalProperties:
                  type: string
    BatchCallResponse:
      type: object
      properties:
        batch_call_id:
          type: string
        name:
          type: string
        from_number:
          type: string
        scheduled_timestamp:
          type: integer
        total_task_count:
          type: integer
    CreatePhoneNumberRequest:
      type: object
      properties:
        area_code:
          type: integer
        nickname:
          type: string
        inbound_agent_id:
          type: string
        outbound_agent_id:
          type: string
        number_provider:
          type: string
          enum:
            - twilio
            - telnyx
    ImportPhoneNumberRequest:
      type: object
      required:
        - phone_number
      properties:
        phone_number:
          type: string
        termination_uri:
          type: string
          description: SIP termination URI for outbound.
        sip_trunk_auth_username:
          type: string
        sip_trunk_auth_password:
          type: string
        inbound_agent_id:
          type: string
        outbound_agent_id:
          type: string
        nickname:
          type: string
    UpdatePhoneNumberRequest:
      type: object
      properties:
        inbound_agent_id:
          type: string
        outbound_agent_id:
          type: string
        nickname:
          type: string
    PhoneNumberResponse:
      type: object
      properties:
        phone_number:
          type: string
        phone_number_pretty:
          type: string
        nickname:
          type: string
        inbound_agent_id:
          type: string
        outbound_agent_id:
          type: string
        area_code:
          type: integer
        last_modification_timestamp:
          type: integer
    Voice:
      type: object
      properties:
        voice_id:
          type: string
          example: 11labs-Adrian
        voice_name:
          type: string
        provider:
          type: string
          enum:
            - elevenlabs
            - openai
            - deepgram
            - play_ht
            - cartesia
        accent:
          type: string
        gender:
          type: string
          enum:
            - male
            - female
        age:
          type: string
        preview_audio_url:
          typ

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# Full source: https://raw.githubusercontent.com/api-evangelist/retell/refs/heads/main/openapi/retell-openapi.yml