list-mailboxes

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

No annotations are provided, so the description carries the burden. It discloses return value details (mailbox names with unread counts and IMAP total counts) and the IMAP-specific behavior. It does not explicitly say 'read-only' or mention permissions, but the 'discovering' and 'listing' language implies a non-mutating operation, which is sufficient for a simple listing tool.

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?

Three focused sentences, each with a clear role ('Use when', 'Returns', 'Do not use when'). No wasted words, and the structure front-loads the primary intent immediately.

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 tool with one optional parameter and an output schema, the description is complete. It covers the purpose, usage context, return behavior, and exclusions, all in a compact format. The existence of an output schema further clarifies the return structure, so no additional detail is needed.

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 input schema has one parameter ('account') with a description that fully covers it (100% schema coverage). The tool description does not add additional semantics beyond what the schema already provides, so the baseline of 3 applies.

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 action ('discovering the mailbox/folder names and unread/message counts') and resource ('available in an account'). It also distinguishes itself from siblings by explicitly stating what it does not do, directing to list-messages/search-messages for message retrieval and list-accounts for account 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?

Provides explicit when-to-use context (e.g., before moving messages or searching a specific mailbox) and when-not-to-use with specific alternative tools. The 'Do not use when' section names two sibling tools, making the guidance actionable and complete.

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