Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden. The verb 'List' / 'Đọc' does communicate a read-only operation and 'monthly invoices' scopes the subject matter, but the description does not disclose pagination, ordering, filtering behavior, or the shape of the returned invoice list.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.