Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds the return shape (JSON array of strings), which is mild added value, but says nothing about error behavior or selector-matching failure modes. A 3 is appropriate with annotations carrying the burden.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.