Dear Haskell-Cafe, I've uploaded a new package named wai-middleware-validation to Hackage. This is a WAI middleware to automate the validation of request and response bodies according to the schema defined in OpenAPI. I hope Web API developers using OpenAPI will give it a try. https://hackage.haskell.org/package/wai-middleware-validation https://iij-ii.github.io/wai-middleware-validation/ Thanks, Kenzo Yotsuya