Folders, accounts and senders

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. 'Changes nothing' largely restates readOnlyHint, and the description adds little beyond annotations apart from noting unread counts are included in the response. With annotations carrying the main burden, 3 is appropriate.

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?

Two compact sentences with no filler; the discovery guidance ('call it first') is front-loaded and the read-only reassurance closes it efficiently.

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?

Despite no output schema, the description enumerates what is returned (accounts, folders with unread counts, sendable addresses) and the zero-required-parameter discovery role. Nothing essential for calling it correctly is missing.

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 description coverage is 100% and the single optional 'account' parameter is fully documented in the schema, including a pointer back to this tool. The description adds no syntax or format detail beyond that, so the baseline 3 for high schema coverage 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?

States a specific verb (Returns) and three concrete resources (accounts, folders with unread counts, send-from addresses). This is clearly distinguishable from siblings like mail_search_emails or mail_get_email, which operate on messages rather than mailbox structure.

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 the agent when to call it: 'Call it first when you do not know which folders or accounts exist.' This is a clear discovery-use condition. It doesn't name alternative siblings or state when NOT to use it, so it falls short of a 5.

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