Do you know any formats/specifications for describing asynchronous interactions?

Asynchronous interactions are often described using several formats and specifications:

• AsyncAPI — an open standard similar to OpenAPI but designed for event-driven and asynchronous APIs. It allows documenting message channels, protocols, data schemas, etc.

• OpenAPI with Webhook support — although primarily for synchronous REST APIs, recent versions include the ability to describe webhooks, partially covering asynchronous scenarios.

• WSDL with WS-Addressing and WS-Eventing support — for SOAP services that involve asynchronous calls and events.

• Protocol Buffers with gRPC — gRPC supports streaming and asynchronous calls, although the specification itself does not describe interactions but rather the format and protocol.

• BPMN (Business Process Model and Notation) — for modeling business processes, including asynchronous messages and events.

Example of using AsyncAPI (fragment):

asyncapi: '2.0.0'
info:
  title: Example Async API
  version: '1.0.0'
channels:
  user/signedup:
    subscribe:
      message:
        payload:
          type: object
          properties:
            userId:
              type: string