Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, openWorld and non-destructive, yet the description adds real behavioral context beyond them: JavaScript is rendered in a real browser, so results differ from a plain fetch, plus the cost model ($0.005 per successful call, failures free) and an unauthenticated free tier. These are operational facts an agent cannot infer from structured fields.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.