Apply labels to a thread

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

Annotations indicate idempotentHint=true and destructiveHint=false. The description adds that labels are applied to 'every message in a Gmail thread,' which is important behavioral context beyond annotations. No annotation contradictions. However, it does not mention error conditions or permissions, which would improve transparency.

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 a single sentence (16 words) with a concise hint. It is front-loaded with the purpose and contains zero wasted words. Ideal brevity.

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 straightforward mutation operation, three required parameters with full schema coverage, and annotations, the description is complete. It states what the tool does and where to get label IDs. For a tool with no output schema, it suffices. Minor omission: no mention of idempotency or potential side effects on conversations.

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% with clear descriptions for all three parameters. The overall description adds 'Label IDs come from list_labels,' which reinforces the account parameter's hint to call list_accounts. The schema does most of the work, so the description provides marginal added value.

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 title and description clearly state 'Apply labels to a thread.' It specifies applying one or more existing labels to every message in a Gmail thread. The verb 'apply' and resource 'labels to thread' are distinct, and the tool is clearly differentiated from siblings like label_message (single message) and unlabel_thread (remove 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 notes that label IDs come from list_labels, implying a prerequisite. However, it does not explicitly state when to use this tool versus alternatives (e.g., label_message for a single message) or provide when-not-to-use guidance. The context is adequate but not explicit.

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