OpenAPI: Webhook Event Delivery Definition

Documenting Webhooks in OpenAPI

Webhooks are server-to-server HTTP callbacks that notify external systems when events occur. OpenAPI 3.1 introduced a dedicated webhooks section, but you can document them in 3.0 using callback objects or by defining the expected payload schemas.

Webhook Endpoint (Receiver)

Document what the consumer's endpoint should accept:

paths:
  /webhooks/receive:
    post:
      summary: Receive webhook events
      description: |
        Your server should expose this endpoint to receive
        webhook events. Verify the X-Webhook-Signature header
        before processing.
      parameters:
        - name: X-Webhook-Signature
          in: header
          required: true
          schema:
            type: string
          description: HMAC-SHA256 signature for payload verification
        - name: X-Webhook-Event
          in: header
          required: true
          schema:
            type: string
            enum:
              - order.created
              - order.updated
              - payment.completed
              - payment.failed
          description: The event type
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/WebhookPayload'
      responses:
        '200':
          description: Event received and acknowledged
        '400':
          description: Invalid signature or payload

Webhook Payload Schema

components:
  schemas:
    WebhookPayload:
      type: object
      required:
        - id
        - event
        - timestamp
        - data
      properties:
        id:
          type: string
          description: Unique event ID for idempotency
        event:
          type: string
          description: Event type (e.g., order.created)
        timestamp:
          type: string
          description: ISO 8601 timestamp
        data:
          type: object
          description: Event-specific payload data

Signature Verification

Document the signature algorithm: typically HMAC-SHA256 of the raw request body using a shared secret. Include example code or reference your SDK documentation for verification.

Retry Policy

Document your retry behavior: how many times you retry failed deliveries, the backoff strategy (exponential, fixed intervals), and the timeout window. This is critical information for webhook consumers to implement proper handling.