list_mailboxes

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is clear. The description adds useful ordering ('newest first') and scoping behavior (single mailbox vs all account). However, it doesn't disclose pagination limits, data freshness guarantees, or what happens if API key is invalid.

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 sentences, each serving a distinct purpose (what, when, edge cases). Slightly verbose in the second sentence, but no wasted words. Could merge scoping info into first sentence for better front-loading.

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 zero parameters, no output schema, and annotations covering safety/idempotency, the description fully addresses what an agent needs: purpose, usage guidance (including when to call first), scope behavior, and empty list handling. No gaps remain for this simple tool.

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?

Schema has 0 parameters (100% coverage), so the description need not add param info. The description still adds meaning by specifying output structure (id, email) and behavior not in schema (newest first, scoping rules), going above baseline 3.

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 provides a specific verb ('List') and resource ('mailboxes') with clear behavioral details (newest first, what each returns). It distinguishes itself from sibling tools like create_mailbox and list_inbox by focusing solely on mailbox enumeration.

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 tells when to use this tool ('first call in a workflow', when you need a mailbox_id) and when not to use alternatives ('check whether you already have a mailbox before creating one', implying create_mailbox is alternative). Also handles edge cases like empty results and API key scoping.

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