Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety bar is low. The description still adds real value by stating that the page is 'public' (no auth needed) and that the response is raw markdown, which tells the agent what format it gets back rather than rendered HTML.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.