Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish that this is a safe, read-only, idempotent operation. The description adds useful behavioral context beyond that: tokenization uses cl100k_base with an approximate character-per-token ratio, and overlap is optional. It does not discuss error behavior or output structure, but the output schema covers the latter.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.