List mailboxes

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

The description adds useful behavioral context: the operation is fast and uses pre-maintained counts, and it lists the output fields. However, it says 'Every mailbox' while the optional limit parameter caps results, and it does not disclose ordering or pagination behavior. With no annotations, this is a moderate disclosure.

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 extremely concise, with the main purpose front-loaded in the first sentence. The second and third sentences are short and add relevant performance and data-source context without fluff.

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 tool, the description covers the returned fields (account, message count, unread count) and a performance trait. The primary gap is the inconsistency with the limit parameter, but the schema covers that. Overall, it is nearly complete for this tool's complexity.

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?

The schema already provides a clear description for the limit parameter ('Maximum results. Capped at 200.'), so the baseline is 3. The description adds no additional parameter meaning and could even be misleading with 'Every mailbox' given the limit cap.

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 every mailbox with its account, message count, and unread count. The title 'List mailboxes' provides a specific verb+resource, and the description's detail on returned fields distinguishes it from sibling tools like list_accounts and get_emails.

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: use this tool to quickly retrieve mailbox overviews with counts. It mentions 'Fast' and that counts are maintained by Mail, which gives contextual guidance. However, it does not explicitly name alternatives or conditions for when not to use it.

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