Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries full burden. It transparently states what the tool returns at a high level (inputs, outputs, assumptions, tables) and it is safely implied to be non-mutating, but it does not explicitly say it performs no calculation or expose other behavioral traits such as read-only status or formatting of the description.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.