Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden itself. It discloses the recomputation behavior, the first-divergent-index report, field-based kind detection, and important byte-exactness and float-vs-integer caveats. It could say what happens when all links match, but the output schema likely covers return details.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.