Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds useful behavioral detail beyond that: the response is a ranked list of phrases, each carrying the live result count it would return. It doesn't discuss rate limits or the limit parameter's effect, but the added return-value insight is real value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.