> ## Documentation Index
> Fetch the complete documentation index at: https://docs.custral.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Append a message

> Append a single message to a conversation, fanning it out to any teammate watching live. **Requires scope:** `conversations:write`.



## OpenAPI

````yaml /openapi-v1.json post /v1/conversations/{id}/messages
openapi: 3.1.0
info:
  title: Custral API
  version: v1
  description: >-
    The curated, versioned, API-key-authenticated public REST surface (`/v1`).
    Every endpoint here is what the official SDKs (`@custral/sdk`) and the MCP
    server are built on. Authenticate with a secret API key (`sk_…`) created in
    **Settings → Applications**.
  contact:
    name: Custral Support
    email: hello@custral.com
    url: https://custral.com
  license:
    name: Proprietary
    url: https://custral.com
servers:
  - url: https://api.custral.com
    description: Production
security:
  - ApiKey: []
tags:
  - name: Identity
    description: Introspect the calling API key.
  - name: Records
    description: Create, list, retrieve, and update records on any object.
  - name: Objects
    description: Read the object (table) schema of your workspace.
  - name: Conversations
    description: View, manage, and ingest conversations and their messages.
  - name: MCP
    description: Introspect the Model Context Protocol tool surface for a key.
  - name: Documents
    description: Read record notes / page documents as markdown.
paths:
  /v1/conversations/{id}/messages:
    post:
      tags:
        - Conversations
      summary: Append a message
      description: >-
        Append a single message to a conversation, fanning it out to any
        teammate watching live. **Requires scope:** `conversations:write`.
      operationId: appendMessage
      parameters:
        - name: id
          in: path
          required: true
          description: The conversation id (`conv_…`).
          schema:
            type: string
          example: conv_123
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/AppendMessageBody'
      responses:
        '200':
          description: The created message.
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    $ref: '#/components/schemas/Message'
                  reqId:
                    $ref: '#/components/schemas/RequestId'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '403':
          $ref: '#/components/responses/Forbidden'
        '404':
          $ref: '#/components/responses/NotFound'
components:
  schemas:
    AppendMessageBody:
      type: object
      description: One message to push into a conversation.
      properties:
        text:
          type: string
          example: On my way!
        author:
          type: string
          description: Display name of the sender.
        authorId:
          type: string
          description: Stable handle of the sender (phone, email, record id).
        direction:
          type: string
          enum:
            - inbound
            - outbound
        timestamp:
          type: string
          format: date-time
          description: ISO 8601. Defaults to now.
      required:
        - text
    Message:
      type: object
      description: A single transcript message.
      properties:
        id:
          type: string
          example: msg_123
        text:
          type: string
          example: On my way!
        author:
          type:
            - string
            - 'null'
          description: Display name of the sender.
          example: Jane Doe
        authorId:
          type:
            - string
            - 'null'
          description: Stable handle of the sender (phone, email, record id).
          example: '+15551234567'
        sourceType:
          type:
            - string
            - 'null'
          example: imessage
        direction:
          type:
            - string
            - 'null'
          enum:
            - inbound
            - outbound
            - null
          example: inbound
        timestamp:
          type:
            - string
            - 'null'
          format: date-time
      required:
        - id
        - text
    RequestId:
      type: string
      description: >-
        A per-request id (`req_…`). Quote it to support when reporting a
        problem.
      example: req_2a1f9c8e7b6d5
    Error:
      type: object
      description: >-
        The failure envelope. Every error carries a machine-readable `code` and
        the `reqId` of the failing request.
      properties:
        error:
          type: object
          properties:
            code:
              type: string
              example: insufficient_scope
          required:
            - code
        reqId:
          $ref: '#/components/schemas/RequestId'
      required:
        - error
  responses:
    Unauthorized:
      description: >-
        The API key is missing, unknown, inactive, or expired (`code:
        invalid_api_key`).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              code: invalid_api_key
            reqId: req_2a1f9c8e7b6d5
    Forbidden:
      description: >-
        The key lacks the scope this endpoint requires (`code:
        insufficient_scope`).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              code: insufficient_scope
            reqId: req_2a1f9c8e7b6d5
    NotFound:
      description: 'The object or record was not found (`code: not_found`).'
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
          example:
            error:
              code: not_found
            reqId: req_2a1f9c8e7b6d5
  securitySchemes:
    ApiKey:
      type: http
      scheme: bearer
      bearerFormat: sk_...
      description: >-
        A Custral **secret** API key (`sk_…`), created in Settings →
        Applications. Sent as `Authorization: Bearer sk_…`. The `X-Api-Key:
        sk_…` header is also accepted and takes precedence. Never expose a
        secret key in a browser.

````

## Related topics

- [The Conversation object](/dev/api-reference/conversations.md)
- [Slack](/integrations/slack.md)
- [Forms](/comms/forms/overview.md)
- [Nylas](/integrations/nylas.md)
- [email.received](/dev/webhooks/events/email-received.md)