Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The schema coverage is 100%, describing each parameter and its source. The description adds the clarification that list_id and list_name are mutually exclusive alternatives ('Pass this OR list_name'). This adds meaning beyond the schema descriptions, which already are detailed. The description doesn't add anything about person_id beyond what the schema says, but the schema is sufficient, so a baseline of 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.