Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds context beyond annotations by noting 'Requires authentication' and stating that it 'Creates a session' and returns a session_id. It also describes the tracking scope (all tool calls, model calls, decisions, errors). Annotations already indicate non-read-only, so no contradiction; the description complements them.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.