Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly and idempotent, but the description adds important context: keyless access (Yahoo Finance), return fields (current price, previous close, change, daily % change), and accepted symbol formats (^, =X). This goes beyond annotations without contradicting them.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.