Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Despite readOnlyHint=false, the description explains the write-on-first-call/stored/cached-read behavior that justifies that annotation, plus a precondition (website must have a description or the mention returns unchanged) and the null-not-404 edge case. These are exactly the traits annotations cannot convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.