List messages

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

With no annotations, the description must carry the burden of behavioral disclosure. It does so well: clarifies performance (never opens message files), return behavior (opaque keys, not row numbers), ordering (newest first), and filtering (deleted excluded). It does not mention auth or rate limits, which are expected to be handled elsewhere.

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 three concise sentences. The first conveys the main purpose and filters, the second adds performance and safety context, and the third clarifies return keys and deleted-message behavior. No wasted words.

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?

With no output schema, the description explains the return format sufficiently by stating 'opaque message keys' and how they differ from row numbers. It does not detail other returned fields, but the sibling tool get_email likely consumes these keys. For a listing tool with 5 optional parameters, this is adequately complete.

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 100%, so each parameter is already documented. The description adds context by grouping filters (unread, flagged, mailbox, date) and noting the 'date' filter corresponds to 'after', but this adds minimal value beyond the schema.

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 clearly states the tool lists messages ('List messages') and specifies scope: recent messages, newest first, with filters. It distinguishes itself from siblings like get_email (which fetches a single message) and search by focusing on catalogue-based listing.

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 implies usage for filtered listing and highlights speed ('reads Mail's own catalogue') but does not explicitly contrast with alternatives like search or get_email_links. No exclusions or when-not-to-use guidance, but the purpose and filters make intended usage clear.

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