Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden. It discloses that this is an authenticated read operation over all letters for a key, but it does not say whether reading consumes letters, what failure modes exist, or what the response contains. 'Read' implies no side effects, yet the auth step and lack of return-value detail leave gaps.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.