APIs.json is a discovery format I created. A provider publishes a small index file at a well-known location on their own domain, and that file describes their APIs plus all the operations around them — the documentation, the OpenAPI definitions, the terms of service, the pricing page, the support channels, the status page, the SDKs, the change log.
The design principle is decentralization. Rather than a central directory somebody has to maintain and keep accurate, the index of the API economy emerges from what providers publish about themselves. It is the sitemap idea applied to APIs, and after more than a decade I still think it is basically the right architecture for discovery.
I will be honest that it never got the adoption I hoped for. The reason is the reason most discovery formats struggle: the benefit accrues to the ecosystem while the work falls on the individual provider, and providers with a marketing site and a docs portal do not feel the pain that the format solves.
Two things have changed the calculus. Inside a large organization, an APIs.json per team turns “who owns this and where is the contract” from an archaeology project into a fetch. And agents need exactly this: a machine-readable pointer to the contract, the terms, the auth, and the support channel. The format was built for machine consumers before there were many worth building for.
