Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100%, so a 3 is the floor, but the description earns more by supplying candidate status values ("completed", "failed", "running") where the schema has no enum, and by naming where agent_id comes from (save_agent/list_agents). Only limit is left to the schema, which documents it adequately.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.