APIs.json is a machine-readable specification that allows API providers to describe their API operations. It serves as an index of internal, partner, and public APIs, providing both machine-readable artifacts like OpenAPI, JSON Schema, and more, as well as human-readable elements like documentation, pricing, and terms of service. The latest version of APIs.json is 0.16, with older versions available as well. An example APIs.json file is provided, showcasing the capabilities of the API discovery specification. The file includes information about a specific API, such as its name, description, image, human URL, base URL, tags, and contact details. It also contains properties like signup, documentation, OpenAPI, JSON Schema, blog, and pricing URLs. The APIs.json file supports inclusion of other APIs as well. The maintainers of APIs.json include Kin Lane, who can be contacted through email or Twitter. For those interested in contributing or participating in discussions about APIs.json, there are GitHub Issues and a Google Group available.