list_mailboxes

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

With no annotations, the description must disclose behavioral traits on its own. It explains that each mailbox has an address and that the tool is a prerequisite for other operations, but it does not explicitly state whether the operation is read-only or free of side effects. It also omits any mention of potential large result sets or output format, leaving some behavioral expectations implicit.

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 sentences with no filler. The first sentence states the core action and context; the second explains the practical purpose (discovering IDs). Information is front-loaded and every clause earns its place.

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 with no parameters and no output schema, the description covers the essential points: what is listed (mailboxes), ownership (authenticated account), and why it matters (IDs for other tools). It does not describe the result shape or pagination, but that is a minor gap given the low complexity and the fact that no output schema is provided.

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% and there is nothing to document. The description adds valuable usage context (that this is a first-step discovery tool) beyond the empty schema, which is appropriate. The baseline of 4 for zero-parameter tools 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 states a specific verb ('List') and resource ('mailboxes'), and clarifies scope ('available to the authenticated account'). It explicitly positions the tool as a discovery step ('Call this first to discover mailbox IDs'), which distinguishes it from sibling tools like get_message or send_email that operate on messages rather than mailboxes.

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 gives explicit timing guidance: 'Call this first' to obtain IDs needed by other tools. This clearly instructs the agent when to use it and why, eliminating ambiguity about its role relative to the sibling tools. No exclusions are needed since the purpose is self-evident.

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