Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare a non-read-only, open-world, non-destructive operation, so the agent already knows this is a mutating external call. The description adds that credentials come from the system keychain, which hints at an OS-level prompt, but it never says whether a session token is stored, how long it lasts, or what a failed login looks like.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.