API OpenAPI Callbacks and Webhook Definitions

Status: public · Confidence: medium (0.865) · Basis: verified_sources

## 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)