Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations (readOnlyHint, openWorldHint, destructiveHint), the description adds valuable behavioral context: it is purely keyword-based, runs offline, does no reasoning, and has known recall gaps ('misses anything the keyword table does not name'). This goes beyond what annotations provide and sets accurate expectations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.