list_folders

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

No annotations are supplied, so the description carries the full disclosure burden, and it does substantial work: it declares the default scope (top-level), the override mechanism, and the per-folder metrics returned. What it omits is whether counts are cheap or expensive to compute and whether there is any pagination or result cap on large mailboxes — relevant for an agent iterating folder trees. 'List' makes the non-mutating nature clear enough that no contradiction exists.

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 earning its place: return shape first, scoping rule second, routing guidance third. The default behavior is front-loaded before the alternative, so an agent skimming gets the operative constraint immediately.

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 one-optional-parameter read tool with an output schema present, nothing essential is missing — the description covers default scope, the override, and when to prefer a sibling, and need not restate return structure. The only residual gap (enumerating well-known folder names) is minor at this complexity level.

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 coverage is 0%, so the description must compensate for the single parameter, and it does: 'parent' accepts either a folder id or a well-known name, and null means top-level. That is genuine meaning beyond the bare string-or-null schema. It stops short of naming which well-known names are accepted (e.g. INBOX, SENT), which is the remaining ambiguity an agent would hit.

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 and resource ('List mail folders') plus exactly what each entry carries (ids, unread/total counts, subfolder counts), and distinguishes itself from mailbox_overview by framing that sibling as the size-ranking alternative. An agent can tell it apart from list_messages, create_folder, and mailbox_overview without opening a schema.

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?

Gives explicit default behavior (top-level only) and the condition that changes it (pass parent to list inside it), then names four concrete downstream consumers of the returned folder id (list_messages, move_messages, create_folder, create_rule). It also names the alternative and the condition selecting it: for sizing a cleanup, use mailbox_overview instead.

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