In the /tags route, the following information is returned for a specific tag:

{
  "name": "c#",
  "count": 262613,
  "is_required": false,
  "is_moderator_only": false,
  "has_synonyms": true
}

is_required indicates that the tag is part of the set of required tags for the site. This is great, but leads to problems when trying to indicate this using the data returned from the /questions route. The only data returned by this route is the tag name. Currently there is no method to fetch additional data for a specific tag.