TypeScript types and JSON schemas
As developing for H5P can be a bit daunting for newcomers, I've started creating TypeScript type definitions for the H5P core and JSON schemas that cover semantics.json and library.json. If you add them to your IDE or build process, you get (partial) code completion. The docs and files can be found here: https://github.com/sr258/h5p-types
This is an ongoing project and it's not finished yet, but maybe it's already helpful for some people.