The catalog now carries 1,768 AsyncAPI definitions. The events rollup resolves them into 4,753 channels across 661 providers, browsable at apis.io/channels/.
Set that against the OpenAPI side of the house and the asymmetry is the story. We index more than 25,000 providers. Fewer than 700 of them describe their event surface in a machine-readable way. Every one of the other 24,000-odd sends webhooks that you discover by reading prose, or by triggering one and capturing what lands.
Who actually publishes it
By volume of definitions, the leaders are Amazon and Adobe (4 each), then Microsoft, Coinbase, and Apache (3 each), with Zoom, Upwind, Sequence, Veho, Trellis, and Spare among the two-definition tier.
That list is more interesting for its composition than its size. It is not the usual cast of API-first names. Coinbase is there because crypto markets are event-native — a price feed is a stream. Apache is there because message infrastructure projects describe channels as a matter of course. Amazon and Microsoft are there because their event services are products in their own right.
Notably absent from the top: most of the SaaS providers whose entire integration story is webhooks.
Why the gap persists
An OpenAPI definition pays for itself immediately — it generates SDKs, powers documentation, drives a try-it console. The provider sees the return.
An AsyncAPI definition mostly pays the consumer. It tells you what will arrive, on which channel, in what shape, before you have written a listener. The provider’s incentive is weaker, so it does not get done, and the cost lands downstream as every integrator independently reverse-engineers the same payloads.
This is the single largest structural gap in the catalog. Not missing OpenAPI — that battle is substantially won. Missing event descriptions.
What a good one looks like
The pattern worth copying, visible in the providers who do this well: define the channel, name the message, bind the schema, and version the whole thing alongside the REST definition rather than in a separate doc that drifts. Adyen — profiled today at 202 APIs — goes further and treats its webhook surfaces as separately-specified APIs rather than as an appendix to the payments docs.
Where a provider ships both an OpenAPI and an AsyncAPI for the same product, an integrator can see the full loop: the call they make, and the event that comes back. That is the whole point.
Takeaway
1,768 definitions, 4,753 channels, 661 providers — against a catalog of more than 25,000. Event-driven description is where API discoverability was a decade ago. If you publish webhooks and do not publish an AsyncAPI, you are asking every one of your integrators to guess.
Browse the event surface at apis.io/channels/.