APIs are becoming a crucial part of the Web. Unfortunately however, it remains very difficult to determine the location of these APIs on servers around the Web. The only way to discover APIs and their properties is via human driven search through public search engines or in hand curated API Directory listings. While these methods work, neither can scale to the potentially hundreds of thousands and millions of APIs which will be published over the next few years.
Further, any means of finding APIs - directory or search struggles with keeping information up to date.
The objective of APIs.json is to help fix this problem by making it easy for people to signpost where the APIs on a given domain are and provide information on how they work. The format is simple and extensible and can be put into any web root domain for discovery.
More information is on the format page.
You can check out a simple search engine using APIs.json live at APIs.io. The code for the search engine is also open source, so you can run your own!
If you have comments on the format, search or anything related, discussion is here on the APIs.json Google Group.
Also see a related effort: APICommons.