A struct can also host a specific set of JSON data; all of the exported keys will have names identical to the respective fields. In order to customize the keys, Go enables us to follow field declarations in a struct with a string that should contain metadata about the field.

These tags take the form of colon separated keys/values. The value is a quoted string, which can contain additional information added using commas (such as job,omitempty). If there is more than one tag, spaces are used to separate them. Let's see a practical example that uses struct tags:

type Character struct {
    Name        string `json:"name" tag:"foo"`
    Surname     string `json:"surname"`
    Job         string `json:"job,omitempty"`
    YearOfBirth int    `json:"year_of_birth,omitempty"`
}

This example shows how two different tags can be used for the same field (we have both json and foo), and it shows how to specify a particular JSON key and introduce the omitempty tag that is used for output purposes to avoid marshaling the field if it has a zero value.