Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world, so the safety profile is covered. The description adds useful context beyond that: the OAuth-dependent behavior of modelId and a hint that this is the discovery step before refining axis ids. No limits or auth caveats beyond OAuth, hence not a 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.