Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare readOnlyHint and openWorldHint, so safety is partly covered; the description adds genuinely new context the annotations do not: the ~6 hour crawl cadence that this tool bypasses, and an authorization/eligibility requirement. It omits cost, rate-limiting, and what happens on repeated calls.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.