Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare readOnlyHint=false, destructiveHint=false, openWorldHint=false, so the agent knows this is a mutating but non-destructive local operation. The description adds value beyond that: changes are scoped to an owned preview window, values are validated before being applied, and the source/default configuration is left untouched — key behavioral facts the annotations do not convey. Error behavior and any permission requirements remain unstated.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.