List accounts

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

Annotations already cover read-only/idempotent/non-destructive, but the description adds substantial context: it reads only the local copy, never contacts a mail server, and reports folder freshness and synchronization status. It also clarifies what it does not return (no mail, no server address, no credentials).

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 sentences, each dense with useful information. It front-loads the primary purpose, then adds usage context, behavioral details, and exclusions without redundant or vague language.

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?

Given the tool's simplicity (no params, output schema present, annotations cover safety), the description fully covers what, when, and what to expect from the output. It explains the significance of synchronization state and explicitly lists what the tool does not return, making it complete for an agent to decide invocation.

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 takes zero parameters, so the description cannot add parameter meaning; baseline for 0 params is 4. The description does explain that each account has an identifier and display name, which may be useful for subsequent calls, but this is not strictly parameter semantics.

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 a specific action: 'Lists the mail accounts this MailFathom deployment serves.' It distinguishes from sibling tools (get_email_content, search_emails, list_emails) which focus on emails, not account metadata.

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?

Explicitly instructs when to use the tool: 'Call it to learn which mailboxes exist and what to call them before narrowing a listing, a search, or a question to one.' It also communicates an implicit exclusion by noting it 'never contacts a mail server,' so it is not for live data.

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