The Commons recon service should have some proper checks on the parameters supplied by the user, and should output meaningful error messages when the API call is ill-formed. The HTTP status code should be set accordingly.

This requires a review of all the routes and adding the necessary checks on the parameters, with appropriate error messages.

For instance, submitting an invalid JSON blob as reconciliation query currently returns an HTTP 500 error:
https://commonsreconcile.toolforge.org/en/api?queries={%22q0%22