Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish read-only, idempotent, non-destructive behavior, so the bar is lower. The description adds meaningful context beyond annotations: the LCS algorithm, line-count output, formatted hunks, and configurable context lines, though it does not mention limitations such as line-oriented rather than word-oriented comparison.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.