Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower, and the description adds a genuine authorization disclosure: 'Discovery never grants access.' It also surfaces the fallback behavior. However, it says nothing about what the response shape or pagination looks like, so it's not fully complete.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.