Package validator validates the fields of structs by applying the rules embeded in a fields "validate" tag to the value of that field. It is designed to return plain english error messages that refer to field names by their json key. These validation error messages are intended to be presented to the outside world. Rules can be joined together with "and"s (&) and "or"s (|) Comma seperated params can also be passed to a rule, but not every rule has parameters. Check the godoc of the spefic rule you're applying for an example of how to use it. Finally, its worth noting the validators can cross reference other fields.