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

Annotations already supply idempotentHint=true, readOnlyHint=false, and destructiveHint=false, so the description does not need to repeat those. It adds the useful context that only name and color can be updated on an existing label. However, it does not describe what happens on success, what the response contains, or error behavior, so it stays at the baseline for annotation-covered behaviors.

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 with no wasted words. The first sentence states the action and scope, and the second sentence provides the usage trigger. Information is front-loaded and 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 update tool with one required parameter, 100% schema coverage, and adequate annotations, the description covers the core usage context. The main omission is what happens after a successful update (e.g., return value or side effects), but given the absence of an output schema and the tool's simplicity, this is a minor gap rather than a blocking one.

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%, and each parameter already has a clear description in the schema. The tool description mentions 'name or color', which loosely maps to two parameters, but it does not add additional semantic meaning beyond what the schema already provides. The baseline of 3 is appropriate.

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 ('Update') and resource ('existing label') and narrows the action to changing its name or color. It is clear, though it does not explicitly contrast itself with create_label or delete_label beyond the word 'existing', so it falls short of full sibling differentiation.

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 gives an explicit trigger condition: 'Use this when the user wants to rename or recolor a label.' This tells an agent when to select the tool. It does not provide exclusion criteria or mention alternatives, but the trigger is sufficiently clear for a focused update tool.

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