AsyncAPI is an open specification for defining and documenting event-driven and asynchronous APIs in a machine-readable format. It describes message channels, payloads, bindings, and operations across protocols such as Kafka, MQTT, AMQP, and WebSockets, enabling tooling, code generation, and documentation.
AsyncAPI
AsyncAPI is the open specification for describing event-driven and asynchronous APIs in a machine-readable way — the counterpart to OpenAPI for the world of messages, streams, and events rather than request-response. It documents the channels a system publishes and subscribes to, the shape of the messages that flow through them, and the protocol bindings that carry them, so that the same document can drive documentation, code generation, and validation. It was created in 2017 and now lives under the Linux Foundation alongside the other core API specifications.
- Channels, messages, and operations - The spec describes what a service publishes and consumes, not just endpoints you call.
- Protocol-agnostic bindings - One document can cover Kafka, MQTT, AMQP, WebSockets, and more through protocol-specific bindings.
- Shared schema tooling - Payloads are defined with JSON Schema, so message contracts reuse the same modeling as the rest of the API stack.
- Full tooling ecosystem - Generators, validators, and documentation renderers turn the contract into working artifacts.
In real API operations, AsyncAPI is how a provider makes its streaming and event surface as governable as its REST surface — and in the sectors I score, its absence is conspicuous. Across banking and market data, the mandated or documented request-response pipes are covered while the event side goes undescribed, leaving roughly half the artifact family unbuilt. As agents begin to consume real-time and event-driven APIs, an AsyncAPI document is what makes that surface discoverable and safe to automate against rather than a black box.
Open source tools that implement this standard
Harvested from this standard's own governing organisation, with the license read from each repository rather than assumed. The role is what the tool does to the specification, from the shared vocabulary — so an agent holding one of these documents can resolve straight from a goal to a tool.
| Tool | Role | License | What it does |
|---|---|---|---|
| Microcks | mocks |
Apache-2.0 | A mocking and contract-testing platform that imports OpenAPI, AsyncAPI, gRPC and Postman artifacts and serves mocks plus confor... |
| AsyncAPI Generator | generates |
Apache-2.0 | Generates documentation, code and configuration from an AsyncAPI document using a template system — the output is whatever temp... |
| Modelina | generates |
Apache-2.0 | Generates typed data models from AsyncAPI, OpenAPI, JSON Schema and other inputs — models only, deliberately not a whole applic... |
| Specmatic | tests |
MIT | Executes contracts for both testing and mocking, and is the only Arazzo implementation that will span REST and events in a sing... |
| Springwolf | generates |
Apache-2.0 | Generates an AsyncAPI document from a running Spring Boot application by inspecting its listeners and publishers — code-first r... |
| AsyncAPI CLI | validates |
Apache-2.0 | The single entry point to the AsyncAPI toolchain — validates, converts, bundles, diffs and generates from AsyncAPI documents, a... |
| AsyncAPI React Component | documents |
Apache-2.0 | A React component that renders AsyncAPI documents as interactive documentation inside an existing application. |
| AsyncAPI Studio | authors |
Apache-2.0 | A visual editor for AsyncAPI documents with live validation and a rendered preview of the event-driven architecture being descr... |
| AsyncAPI Parser | parses |
Apache-2.0 | Parses and validates AsyncAPI documents into a stable intermediate model, resolving references — the library every other AsyncA... |
Referenced on the API Evangelist blog
Where this standard shows up across sixteen years of my writing at apievangelist.com — how it fits into API design, governance, and the agentic turn.
AsyncAPI Version 2.0 Is Ready For Use
2019-09-11
OpenAPI is the HTTP Binding in AsyncAPI
2020-07-20
