---
id: api-openapi-callbacks-and-webhook-definitions
title: 'API OpenAPI Callbacks and Webhook Definitions'
schema_type: TechArticle
category: computer-science
language: en
confidence: medium
last_verified: '2026-06-03'
created_date: '2026-06-03'
generation_method: ai_structured
derived_from_human_seed: true
conflict_of_interest: none_declared
is_live_document: false
data_period: static
atomic_facts:
  - id: fact-cs-api-openapi-callbacks-and-webhook-definitions-1
    statement: >-
      OpenAPI Initiative documentation says callbacks describe an asynchronous request pattern
      where the API consumer provides a URL for a later response.
    source_title: OpenAPI Providing Callbacks
    source_url: https://learn.openapis.org/specification/callbacks
    confidence: medium
  - id: fact-cs-api-openapi-callbacks-and-webhook-definitions-2
    statement: >-
      OpenAPI Initiative documentation says webhooks support out-of-band events from an API
      provider to an API consumer.
    source_title: OpenAPI Providing Webhooks
    source_url: https://learn.openapis.org/specification/webhooks
    confidence: medium
  - id: fact-cs-api-openapi-callbacks-and-webhook-definitions-3
    statement: >-
      The OpenAPI Specification describes OpenAPI as a standard interface description for HTTP APIs.
    source_title: OpenAPI Specification v3.1.1
    source_url: https://spec.openapis.org/oas/v3.1.1.html
    confidence: medium
completeness: 0.82
known_gaps:
  - A usable webhook contract also needs signing, retry, event identifiers, idempotency, schema evolution, subscription management, and delivery logs.
disputed_statements: []
primary_sources:
  - title: OpenAPI Providing Callbacks
    type: documentation
    year: 2025
    url: https://learn.openapis.org/specification/callbacks
    institution: OpenAPI Initiative
  - title: OpenAPI Providing Webhooks
    type: documentation
    year: 2025
    url: https://learn.openapis.org/specification/webhooks
    institution: OpenAPI Initiative
  - title: OpenAPI Specification v3.1.1
    type: standard
    year: 2024
    url: https://spec.openapis.org/oas/v3.1.1.html
    institution: OpenAPI Initiative
secondary_sources: []
updated: '2026-06-03'
ai_models:
  - gpt-5-codex
---

## TL;DR

OpenAPI callbacks and webhooks let agents discover asynchronous API contracts instead of guessing event payloads from prose.

## Core Explanation

Callbacks attach an out-of-band response to a specific operation, often using a runtime expression to resolve the consumer-provided callback URL. Webhooks describe event requests that the provider may send to a consumer-defined URL outside a single request-response path.

Agents should read callback and webhook definitions for event names, request bodies, response expectations, operation identifiers, schemas, and runtime expressions. They should still inspect provider documentation for retry behavior, signature verification, event ordering, and delivery retention.

## Source-Mapped Facts

- OpenAPI Initiative documentation says callbacks describe an asynchronous request pattern where the API consumer provides a URL for a later response. ([source](https://learn.openapis.org/specification/callbacks))
- OpenAPI Initiative documentation says webhooks support out-of-band events from an API provider to an API consumer. ([source](https://learn.openapis.org/specification/webhooks))
- The OpenAPI Specification describes OpenAPI as a standard interface description for HTTP APIs. ([source](https://spec.openapis.org/oas/v3.1.1.html))

## Further Reading

- [OpenAPI Providing Callbacks](https://learn.openapis.org/specification/callbacks)
- [OpenAPI Providing Webhooks](https://learn.openapis.org/specification/webhooks)
- [OpenAPI Specification v3.1.1](https://spec.openapis.org/oas/v3.1.1.html)