List mail accounts

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

With no annotations, the description carries the full burden. It adds valuable context by explaining that accounts are derived from mailboxes on disk and that empty accounts are omitted, plus a performance note ('Fast'). However, it does not describe the return format or error conditions.

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 two short sentences with the primary action front-loaded. It states what the tool returns and immediately adds a relevant caveat, all in efficient language without 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 zero-parameter list tool with no output schema, the description is mostly complete: it tells what is returned (accounts with mailbox counts) and a key behavioral caveat (empty accounts absent). It could be more explicit about the return fields, but this is minor for a simple list.

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 tool has zero parameters, so schema coverage is trivially 100%. The description does not need to explain parameters; the baseline of 4 applies because there is nothing to add 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 it lists the mail accounts configured on this Mac, including the number of mailboxes per account. This specific verb+resource structure distinguishes it from sibling tools like list_mailboxes 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?

No explicit guidance is given on when to use this tool versus alternatives such as list_mailboxes. The description implies an account-level overview but does not say 'use this when you need account information' or mention any exclusions.

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