The JSON Schema specification includes validation of a number of built-in formats: see https://json-schema.org/understanding-json-schema/reference/string.html#built-in-formats. Drafts 6 and 7 of the JSON Schema extend this built-in format validation. The format keyword was never implemented in MongoDB, so we should add it. MongoDB users may wish to validate that their email addresses, ip addresses, hostnames, URIs, and so on are well-formed with an out of the box implementation.