Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100% for all three parameters, so the schema already documents id, lang, and compact thoroughly. The description adds minimal extra semantics beyond clarifying that the id is a 'slug' and its source (already partially in the schema's enum description). It does not introduce new meaning for lang or compact, so baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.