Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish read-only, idempotent, non-destructive behavior, so the safety profile is covered. The description adds genuine domain context beyond them: what the payload contains (generation chain, size_variants with per-model caveats, buy_links) and two interpretation rules ('Missing size data is unknown', 'Do not apply generation-level battery ranges to individual sizes').
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.