Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (read-only, idempotent, non-destructive). The description adds 'byte-exact', which is a meaningful behavioral guarantee about losslessness beyond the annotations. It does not mention error behavior for invalid Base64 input, but this is a minor gap for such a simple pure function.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.