Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnlyHint/idempotentHint annotations, the description adds meaningful behavioral detail: the ~5min async cadence, the meaning of each next_action state, terminal vs. processing states, and where to find failure reasons or generated roadmap items. This is rich, non-redundant transparency.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.