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

With no annotations provided, the description carries the burden of behavioral disclosure. It discloses the output ('labels with message counts') and scope ('one mailbox'), and the verb 'List' implies a read-only operation. However, it does not explicitly confirm non-destructiveness or mention behaviors like system-label inclusion or pagination.

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 short sentences, both informative. The primary action and output are front-loaded, followed by a helpful analogy. There is no redundancy or filler.

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 simple one-parameter listing tool without an output schema, the description adequately conveys what the agent will receive (labels and message counts) and that the operation is scoped to a single mailbox. It could mention the exact return shape or the read-only nature, but nothing essential is missing for a competent agent to select and invoke it.

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 only parameter, 'mailbox', has 100% schema description coverage including its email format and a pointer to list_authorized_mailboxes. The tool description adds the 'one mailbox' scoping context but does not need to add further parameter-level meaning.

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 every label in one mailbox, with message counts.' This clearly distinguishes it from related tools like create_gmail_label, rename_gmail_label, and apply_gmail_labels, and even adds context by explaining that labels are Gmail's equivalent of 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?

The description makes the listing purpose clear, but it does not explicitly state when to use this tool over alternatives or mention exclusions such as 'to create/modify labels use create_gmail_label/rename_gmail_label.' Usage is implied rather than explicit.

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