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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds that it lists labels across all connected mailboxes and includes both system and user labels, which is useful. However, it doesn't disclose details like whether the response includes label colors or message counts, or how the 'account' parameter affects the result beyond the schema.

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 sentences with no wasted words. The core purpose is front-loaded, and the usage guidance is appended efficiently. Every sentence earns its place.

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 read-only list tool with one optional parameter and no output schema, the description is nearly complete. It explains what is listed, the scope (all connected mailboxes), and when to use it. The only minor gap is not describing the return format, but for a list tool this is acceptable.

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 the schema already documents the 'account' parameter well. The description adds the context that omitting the parameter lists labels for all connected mailboxes, which aligns with the schema. Baseline 3 is appropriate since the schema carries the parameter documentation burden.

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 states a specific verb ('List') and resource ('labels in the user's connected Gmail mailboxes'), and distinguishes system labels from user labels. It clearly differentiates from siblings like get_gmail_message and search_gmail_messages by focusing on label listing.

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 explicitly says 'Use it when the user refers to one of their labels by name,' providing clear context for when to invoke this tool. It doesn't explicitly mention when not to use it or name alternatives, but the use case is specific enough to guide an agent.

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