Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple, two-parameter, idempotent mutation with annotations and no output schema, the description covers all essential decisions: what the tool does, how to target one item, how to target all unread, and that repeated calls are safe. Slight extra detail about the behavior when both `id` and `all` are supplied would be the only remaining improvement, but it is not necessary for a confident call.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.