Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnly, idempotent, non-destructive behavior. The description adds valuable context about state-dependent responses (authenticated:true with empty pending[] vs connect_urls when credentials missing), which is not captured by annotations and aids the agent in understanding expected outputs.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.