See: https://json-schema.org/ and https://swagger.io/specification/ and https://github.com/OAI/OpenAPI-Specification
note: currently there is no built in support for either in Mediawiki Core there are some do not merge patches from a WMDE Dev. See: https://gerrit.wikimedia.org/r/c/mediawiki/core/+/617162 and https://phabricator.wikimedia.org/T221741 this could have been some output of WMDE prototyping week.
Also might be worth looking at https://www.mediawiki.org/wiki/HyperSwitch and RESTbase which are mentioned.
Expected output: An ADR (proposed state) documenting the decision outcome from the investigation