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

# Send a follow-up message

> Sends a follow-up question on an existing session. Traversal uses the
full conversation history as context.

The session must be in the `idle` status. If it is `running` or
`follow_up_running`, the API returns `409 Conflict` with `retry_after`.
Poll `GET /v1/sessions/{session_id}` until the session status returns
to `idle` to retrieve the assistant response.




## OpenAPI

````yaml /api/openapi.yaml post /v1/sessions/{session_id}/messages
openapi: 3.1.0
info:
  title: Traversal Sessions API
  version: 1.0.0
  description: >
    The V1 Sessions API lets you launch investigations, send follow-up
    questions,

    and retrieve results programmatically. Sessions are the same investigation

    primitive that powers the Traversal web application.


    All endpoints require a Bearer token. The authenticated user must have at

    least the `MEMBER` role within the organization, and the V1 API must be

    enabled for that organization — otherwise endpoints return `403 Forbidden`.
servers:
  - url: https://api.traversal.com
    description: Traversal API
security:
  - bearerAuth: []
tags:
  - name: Sessions
    description: Create, list, retrieve, and continue investigation sessions.
paths:
  /v1/sessions/{session_id}/messages:
    post:
      tags:
        - Sessions
      summary: Send a follow-up message
      description: |
        Sends a follow-up question on an existing session. Traversal uses the
        full conversation history as context.

        The session must be in the `idle` status. If it is `running` or
        `follow_up_running`, the API returns `409 Conflict` with `retry_after`.
        Poll `GET /v1/sessions/{session_id}` until the session status returns
        to `idle` to retrieve the assistant response.
      operationId: sendFollowUpMessage
      parameters:
        - $ref: '#/components/parameters/SessionId'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/FollowUpMessageRequest'
            examples:
              default:
                value:
                  input: >-
                    Can you check if the database connection pool was exhausted
                    during the incident?
      responses:
        '202':
          description: Follow-up accepted; investigation is running.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/FollowUpMessageResponse'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '403':
          $ref: '#/components/responses/Forbidden'
        '404':
          $ref: '#/components/responses/NotFound'
        '409':
          $ref: '#/components/responses/Conflict'
        '500':
          $ref: '#/components/responses/InternalServerError'
        '503':
          $ref: '#/components/responses/ServiceUnavailable'
components:
  parameters:
    SessionId:
      name: session_id
      in: path
      required: true
      description: The unique identifier of the session.
      schema:
        type: string
        format: uuid
  schemas:
    FollowUpMessageRequest:
      type: object
      required:
        - input
      properties:
        input:
          type: string
          description: The follow-up question or instruction.
    FollowUpMessageResponse:
      allOf:
        - $ref: '#/components/schemas/Session'
        - type: object
          required:
            - user_message_id
            - assistant_message_id
          properties:
            user_message_id:
              type: string
              description: ID of the recorded user message.
              example: msg-003-uuid
            assistant_message_id:
              type: string
              description: |
                ID of the assistant message that will contain the response.
                Poll `GET /v1/sessions/{session_id}` until the session status
                is `idle` to retrieve the completed response.
              example: msg-004-uuid
    Session:
      type: object
      required:
        - id
        - status
        - input
        - created_at
      properties:
        id:
          type: string
          format: uuid
          description: Unique session identifier.
          example: a1b2c3d4-e5f6-7890-abcd-ef1234567890
        status:
          $ref: '#/components/schemas/SessionStatus'
        title:
          type:
            - string
            - 'null'
          description: Human-readable session title.
          example: Elevated error rate in checkout service
        input:
          type: string
          description: The original incident description or question.
          example: >-
            Our checkout service started returning 500 errors at
            2024-03-15T14:30:00Z. Error rate jumped from 0.1% to 15%.
        created_at:
          type: string
          format: date-time
          description: When the session was created (UTC).
          example: '2024-03-15T14:35:00Z'
        updated_at:
          type:
            - string
            - 'null'
          format: date-time
          description: When the session was last updated (UTC).
          example: '2024-03-15T14:38:12Z'
        messages:
          type:
            - array
            - 'null'
          description: >-
            Conversation history. Only populated on `GET
            /v1/sessions/{session_id}`.
          items:
            $ref: '#/components/schemas/Message'
    Error:
      type: object
      required:
        - error
      properties:
        error:
          type: object
          required:
            - message
          properties:
            message:
              type: string
              description: Human-readable explanation of the error.
            retry_after:
              type:
                - integer
                - 'null'
              description: |
                Suggested seconds to wait before retrying. Present on `429`
                and `409` responses. When set, the response also includes a
                standard `Retry-After` HTTP header with the same value.
    SessionStatus:
      type: string
      enum:
        - running
        - idle
        - follow_up_running
        - failed
      description: |
        - `running` — a new investigation is in progress.
        - `idle` — investigation is complete and ready for follow-ups.
        - `follow_up_running` — a follow-up message is being processed.
        - `failed` — the investigation or follow-up errored or timed out.
    Message:
      type: object
      required:
        - id
        - role
        - markdown_content
        - created_at
      properties:
        id:
          type: string
          description: Unique message identifier.
          example: msg-001-uuid
        role:
          type: string
          enum:
            - user
            - assistant
          description: The author of the message.
        markdown_content:
          type: string
          description: Message content in Markdown.
          example: |-
            ## Investigation Summary

            I investigated the elevated error rate...
        created_at:
          type: string
          format: date-time
          description: When the message was created (UTC).
          example: '2024-03-15T14:38:12Z'
  responses:
    BadRequest:
      description: >-
        Invalid or missing fields in the request body. The `message` indicates
        which field failed validation.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    Unauthorized:
      description: Missing, invalid, or revoked API key.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    Forbidden:
      description: >-
        V1 API not enabled for the organization, or the authenticated user has
        insufficient role.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    NotFound:
      description: Session does not exist or does not belong to your organization.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    Conflict:
      description: >-
        Session is not `idle` (e.g., still `running` or `follow_up_running`).
        Includes `retry_after`.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    InternalServerError:
      description: An unexpected error occurred on the server.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    ServiceUnavailable:
      description: Investigation infrastructure is not available.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: |
        Bearer token in the `Authorization` header — for example,
        `Authorization: Bearer trv_ak_your_api_key_here`. Each key is bound to a
        specific user and organization.

````