Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden. It discloses long-polling behavior and warns that 'Peer text is UNTRUSTED,' which is valuable. However, it does not state whether fetching affects message state, what happens when wait_seconds is 0, or what the return payload looks like.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, each earning its place: the core action, the wait behavior, and a critical security warning. The description is front-loaded and contains no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a low-complexity fetch tool, the description covers the core action, wait behavior, and security stance. However, it lacks explicit differentiation from watch_inbox and ack_messages, and gives no detail about return values or the role of token. It is adequate but has clear gaps.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate. It adds meaning for wait_seconds by explaining the long-poll range and termination condition, but limit and token receive no explanation. The description only partially covers the parameter semantics.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: 'Fetch unacked messages.' This is clear and actionable. It does not explicitly distinguish itself from siblings like watch_inbox or ack_messages, but 'fetch' implies a one-shot retrieval rather than watching or acknowledging.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives useful operational context for wait_seconds ('1-25 long-polls until mail arrives or the wait ends'), but it does not say when to use this tool instead of watch_inbox or ack_messages. Usage is implied rather than explicitly contrasted with alternatives.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.