Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Even though annotations already indicate read-only and idempotent behavior, the description adds valuable conditional details: when all providers are connected it returns authenticated:true and empty pending[], and when credentials are missing it returns connect_url and per-install URLs. This goes beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.