Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare this is read-only, idempotent, and non-destructive, so the description's safety burden is lowered. The description adds the behavior of converting percent-encoded input to plain text and the intended use context, but it does not disclose edge-case behaviors like handling of malformed input, plus signs, or non-UTF-8 encodings.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.