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

The annotations already mark it as read-only, idempotent, and non-destructive, and the description does not contradict that. It adds behavioral context about the meaning of selectable false and how other tools interact with such folders, which goes beyond what the annotations provide.

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 concise, consisting of two sentences that front-load the main purpose and then provide key clarifications. No redundant or extraneous information is present, and the structure is easy to parse.

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 that there are no parameters and no output schema, the description is complete. It explains what the tool returns (list of mailboxes with special-use roles and selectable status) and provides necessary context for interpreting the results, making it sufficient for an agent to use correctly.

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 no parameters, and the schema reflects this with an empty properties object. The description correctly implies the absence of parameters and adds no misleading information, so it fully aligns with the schema.

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 verb 'List' and the resource 'mailboxes' (IMAP folders), and provides specific details about special-use roles and the selectable flag. It distinguishes this tool from siblings like create_folder, move_email, and delete_email by explaining which operations are valid on non-selectable folders.

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?

It gives explicit guidance on when to use the tool (to list all folders) and when not to use certain operations on non-selectable folders (move_email and delete_email won't work), while noting that create_folder can use them as parents. This effectively differentiates from alternative tools and clarifies the intended use case.

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