Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare readOnlyHint=true and openWorldHint=false, so the agent knows it's a safe, non-mutating, local read. The description adds only the list of sensors covered, which is useful but not rich behavioral context (e.g., return format, whether it reflects live or stored config). With annotations covering safety, a 3 is appropriate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.