API Playground: https://metamask.github.io/api-playground/api-documentation
JSON-RPC API provided by MetaMask.
MetaMask dapp developers lack a formal RPC specification. This attempts to document which methods MetaMask supports in a way that's versionable, human-readable and machine-readable. It will improve the accuracy of documentation, API, and clients.
MetaMasks effectiveness as an enterprise-grade application platform depends on its ability to provide a reliable and predictable developer experience.