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

With no annotations, the description carries the full burden. It clearly discloses that only summaries are returned, no body, and that ordering is newest first. This is the key behavioral trait for a list tool. It does not mention pagination or rate limits, but the main surprise (no body) is explicitly addressed.

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?

The description is short but contains a redundant sentence: 'Summaries only, no body. Summaries only — no body.' This duplication wastes a sentence and detracts from conciseness. The first sentence is effective, and the third provides useful guidance, but the repetition is a clear flaw.

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 list tool with no output schema, the description covers the essential points: it returns summaries, excludes body, orders newest first, and points to the single-message tool for full content. It does not detail summary fields or pagination, but these are either self-evident or covered by the schema. The description is adequate for an agent to call it correctly.

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 coverage is 100%, so the baseline is 3. The description adds no information about the parameters beyond what the schema provides; it mentions 'one address' which maps to inbox_id, but that is already in the schema. No additional semantics are provided, so the baseline score is appropriate.

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 uses a specific verb ('List') with a clear resource ('what arrived at one address') and states the ordering ('newest first'). It also explicitly distinguishes itself from the singular message tool by saying 'Summaries only, no body' and directing the user to 'Read one message' for full content, making the purpose unmistakable.

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 implicitly provides usage guidance by stating that to get full text, HTML, and headers, one should read a single message. This clearly signals when to use this list tool versus the alternative, though it does not name the sibling tool explicitly. The guidance is clear and actionable.

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