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

Annotations already declare readOnlyHint and idempotentHint, so the description doesn't need to repeat those. It adds the 'most recent' ordering behavior but doesn't mention pagination details or default limit, which are partially covered in parameter descriptions. No contradictions with annotations.

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?

Single sentence, no fluff, includes natural-language aliases without redundancy. Every word adds value and is easily scannable.

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 simple listing operation, the description is complete. It doesn't have an output schema, but the function's purpose is clear. The sibling list provides context that mail_read and mail_search exist for narrower queries, but the description alone is sufficient for a basic inbox listing.

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% for the three parameters, each with a short description (tag, limit, offset). The tool description adds no additional semantic insight beyond what the schema provides, so baseline 3 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?

Clearly states the verb 'List' and resource 'account's most recent messages', with natural-language aliases 'read my mail, check my inbox'. It differentiates from siblings like mail_read (specific message) and mail_search (filtered search) by emphasizing the inbox listing scope.

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?

Provides enough context to know when to use it ('read my mail, check my inbox'), implying it's for browsing recent messages. It doesn't explicitly contrast with mail_read or mail_search, but the phrasing and sibling names make the distinction clear.

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