I've been working on my json-schema library, recently, and most of the non-reference based test cases are coming together. As part of that, I was using other libraries like quri and local-time for validating data in their respective domains. Since json-schema has a pre-made test suite I was surprised when some tests failed using them, but it turned into an opportunity to help out. I reported the failures, which turned out to be a deviation from the rfc3339 timestamp spec and excessive leniency in validating ipv6 hostnames.
I've been working on the json-schema library to support an openapi library that I'm going to keep on gitlab while it grows, but it already does a certain amount of codegen - both for the server-side and clients. You can see how you can write a server based on an openapi spec file in the example directory and an example of a generated client (for a different api) is the food data library.
Right now, there's a lot to be improved on both sides - there's little or no security implemented, which is required for most apis, and validation via json-schema is still very much a work in progress, but it's cool to see it all coming together.