Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnlyHint=true, idempotentHint=true, destructiveHint=false), so the bar is lower. The description adds value beyond that by disclosing the response scope ('full detail... includes office, party, status, election years, and mailing address'), giving the agent a concrete expectation of what comes back. It doesn't mention behavior for invalid IDs, but that's a minor gap for a simple lookup.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.