Attention developers: Check out the tags API for Highrise.
The tags API allows you to add, update, and delete tags from parties (people and companies), cases, and deals. In the documentation below, the generic "#{subject_type}" text must be replaced in practice with either "people", "companies", "kases", or "deals", and "#{subject_id}" should be the id of the subject (person, company, case or deal) that you want to manipulate or query the tags for.
Related:
Highrise tags help you drill down to specific contacts [Product Blog]
New in Highrise: Improved tags list [Product Blog]