Apply labels to a message

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

Annotations already declare idempotentHint=true and destructiveHint=false, so the description adds minimal behavioral context. It does not clarify whether labels are added to existing ones or replace them, nor does it mention side effects on thread labels or error conditions.

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 two sentences long, with no extraneous words. It is front-loaded and efficiently conveys the essential purpose.

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 and well-covered schema, the description is mostly complete. It explains the action and source of inputs but lacks detail on behavior (additive vs replace) and error handling, which would improve completeness.

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 100% with detailed descriptions. The tool description restates the source of label IDs, which adds marginal value. The schema already provides sufficient meaning for all parameters.

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 verb 'apply', the resource 'labels to a single Gmail message', and specifies that label IDs come from list_labels. It inherently distinguishes from siblings like label_thread (applies to thread) and unlabel_message (removes labels).

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 indicates that label IDs come from list_labels, implying a prerequisite step. It provides clear context but does not explicitly compare with alternatives or state when not to use the tool (e.g., use label_thread for thread-level labeling).

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