Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, so the description must carry the load, and it does add meaning: it explains the provenance of session_id (an earlier result or report URL) and, via 'two saved tests compared', the paired semantics of compare_session_id. It still doesn't state that compare_session_id is optional, so it stops short of full coverage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.