list_labels

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

Annotations include readOnlyHint=true, and the description adds the explicit 'SIDE EFFECTS: none' statement, reinforcing the safe read-only nature. It also provides behavioral context that the listing includes both system and user labels, which is not in the structured annotations. This adds value beyond the annotations without contradicting them.

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?

The description is extremely concise: two short segments ('List all Gmail labels (system + user)' and 'SIDE EFFECTS: none') plus a focused usage clause. It is front-loaded with the core action, with no wasted words, making it easy to parse quickly.

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?

Given the tool's simplicity (no parameters, read-only, output schema exists), the description covers all necessary context: purpose, usage, side effects, and scope. It explicitly mentions the labels' scope (system + user) and when to use it, making it fully complete for an agent to select and invoke correctly.

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 tool has zero parameters, and the schema is empty, so schema description coverage is 100%. With 0 params, the baseline is 4. The description doesn't discuss parameters because none exist, which is appropriate. No additional parameter semantics are needed.

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 clearly states the tool's function: 'List all Gmail labels (system + user).' It uses a specific verb ('List') and resource ('Gmail labels'), and the scope is explicit. This distinguishes it from sibling tools like modify_labels, bulk_modify, and create_label, which perform mutations.

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 includes an explicit 'USE WHEN' clause, specifying appropriate contexts (inspecting mailbox structure, getting exact label names/ids). It also names alternative tools (modify_labels/bulk_modify/create_label) and notes that a lookup is rarely required because they accept plain label names. This is clear guidance on when to use the tool vs. alternatives.

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