Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnly/idempotent/destructive annotations, the description explains the fail-closed backwardation rule, the leakage-safe as-of semantics, the 1-2 day substrate lag, and the constancy of values per scan_date. This gives the agent a clear behavioral model without contradicting 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.