I can, because I use ajv and JSON Schema instead because I can trivially just take those models and use them in OAS3 documents. The web framework I've built on

I can, because I use ajv and JSON Schema instead because I can trivially just take those models and use them in OAS3 documents. The web framework I've built on top of Fastify--and will be open-sourcing soonish--uses pretty simple model and property annotations to let you define your systems in those terms, and I find it to be really flexible and pleasant to work with. EDIT: Also, as mentioned elsewhere in this thread, io-ts is a pretty good option too!