list_mailboxes

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does add value by clarifying the session-scoped nature of the results and implicitly signaling a read-only operation via 'List'. However, it does not disclose return format, what fields each mailbox entry contains, or how 'session' is defined — gaps that matter for downstream chaining to tools like get_messages.

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 a single 9-word sentence that front-loads the verb and resource. Every word earns its place, with no filler, abbreviations, or redundant restatement of the tool name.

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 low complexity (0 parameters, no nested objects, no output schema), the description captures the essential behavior completely. Mentioning the return shape (e.g., addresses or IDs) would be helpful for tool chaining but is not critical for such a simple list operation.

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, and the baseline for 0-parameter tools is 4. The description correctly implies the tool takes no input, and there is nothing further it needs to explain about arguments.

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'), a specific resource ('temporary mailboxes'), and a scope qualifier ('created in this session'). It is easily distinguishable from sibling tools: list_providers targets providers, create_mailbox/delete_mailbox are mutations, and get_messages/get_message target 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 'created in this session' qualifier provides clear usage context — the agent learns that only session-scoped mailboxes are returned and that persistent or previously-created mailboxes are excluded. However, it does not explicitly name alternatives or state when-not-to-use in the way a 5 would require.

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