Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Adds substantial behavioral detail beyond annotations: default shows first 25 cities alphabetically, query enables partial case-insensitive match, response_format can be markdown or json, and returns canonical names plus aliases. The caveat about the default being rarely needed is honest and useful.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.