AsyncAPI
The specification standard for async, event-driven APIs over Kafka, MQTT, WebSockets, and more — the async equivalent of OpenAPI. The ecosystem includes CLI, parser, code generators, and server stub templates. Widely adopted in microservices and streaming architectures.
Swagger / OpenAPI
Swagger UI is the canonical open-source renderer for interactive API documentation from OpenAPI specs, with 28k+ GitHub stars. SwaggerHub adds collaborative API design, versioning, and governance at scale. The de facto standard for REST API specification across the industry.