Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: output varies by feed type (FMP-backed financials/insider/congress data vs. a text preview for uploaded files), which helps the agent anticipate results.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.