Create, rename or delete a label

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

Beyond the annotations (destructiveHint=true, readOnlyHint=false), the description discloses concrete consequences: delete removes the label from every message, messages themselves survive, and the operation cannot be undone. It also states that only provided fields change on update and that system labels are immutable, giving essential behavioral detail.

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 dense but every sentence earns its place: action rules, nested-name example, visibility semantics, deletion consequences, system-label restrictions, and routing to sibling tools. It front-loads the primary verb and resource before going into conditional details.

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?

With three conditional action modes, five parameters, no output schema, and destructive behavior, the description covers every invocation-relevant concern: prerequisites, field-change semantics, multi-message deletion effects, irreversibility, and excluded label types. A correct call can be constructed from the description alone.

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?

Although the schema covers all five parameters, the description adds conditional semantics the schema cannot express: create requires name with optional nesting and an existing parent, update requires label_id plus at least one other field, and delete requires only label_id. It also clarifies what each visibility enum controls in the sidebar versus the message list, materially improving invocation correctness.

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 name a specific resource—user labels—and three explicit operations: create, rename/update, delete. It immediately separates label management from modifying messages by directing to modify_message/modify_thread, so an agent can distinguish it from sibling tools without inspecting schemas.

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 states when not to use the tool ('To apply/remove labels on mail, use modify_message or modify_thread, not this tool') and narrows scope by excluding system labels. It also provides clear action-by-action usage rules, so the agent knows exactly which sibling handles message-level label operations.

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