hi, i notice a problem with the "date-time" format. They guys from spacetelescope say that there example is valid => https://spacetelescope.github.io/understanding-json-schema/about.html?highlight=date%20time but the validator says no :) input: ... { "birthday": "2017-02-22" } json_spec .... "birthday": { "type": "string", "format": "date-time" }, I think your version is correct because RFC3309 doesn't allow that TIME is optional. I don't know whats correct. Can you gimme a hint? Greetz, Majk