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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds useful context beyond that: the enumerated role set (inbox, sent, drafts, trash, archive, spam, custom) and the fact that a call can span all reachable accounts. It does not discuss pagination, but an output schema exists to carry return shape.

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?

Front-loaded with the resource and payload, then usage, then a compact example. Three sentences with little waste, though the example partly repeats the 'account_id' semantics already stated in the schema.

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 two-parameter, zero-required read tool with full schema coverage, annotations, and an output schema, this covers purpose, scope, and the reason to call it. Only marginal gaps (pagination or ordering behavior) remain, and those are plausibly in the output schema.

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%, so both parameters (account_id, profile_id) are already documented. The description's 'for one account or all' mirrors the schema's 'omit for every account' rather than adding new semantics, so the baseline 3 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 (Lists) and resource (folders/Gmail labels) plus the returned fields (role and counts) and scope (one account or all). Clearly distinguishable from mail_list_messages, which it names as a downstream consumer rather than a peer.

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 says to use it to obtain a `folder_id` for mail_move or mail_list_messages, which routes the agent correctly. It stops short of stating when not to use it (e.g., versus mail_list_changes), so it is clear context rather than full when/when-not guidance.

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