Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Adds real behavior beyond the annotations: the first call covers the last 7 days, the per-connection mark is advanced implicitly, own writes are excluded unless include_own is true, and agent-authored text is untrusted and excerpted to 240 characters. It also flags the auth prerequisite (connection key must have a name). The readOnlyHint=false / idempotentHint=false pair is not explicitly explained in the description itself (the mark semantics appear in the since parameter docs), so not a full 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.