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

Annotations already declare destructiveHint=true and readOnlyHint=false, covering the safety profile. The description adds that TxnId cancels all labels for the order, which is a useful behavioral consequence beyond a single label. However, it doesn't disclose failure modes or the Force parameter's effect on unshipped status. With annotations present, this is adequate but not rich.

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, front-loaded with the action, followed by clear selection guidance. It contains zero redundant information and is efficiently structured.

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 5 parameters, no required fields, and an output schema, the description covers the essential selection logic. It doesn't mention the Force parameter or cancellation failure behavior, but these are documented in the schema and annotations. For a cancellation tool, this is reasonably complete.

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%, so baseline is 3. The description adds value by grouping parameters into mutually exclusive alternatives and noting that TxnId cancels all labels, reinforcing schema semantics. This selection logic is not explicitly encoded in the schema, so the description enhances parameter understanding.

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 'Cancel a purchased shipping label' with a specific verb and resource, clearly distinguishing it from sibling tools like purchase_label and track. The action and target are unambiguous.

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 provides explicit selection guidance: 'Provide one of: TxnId, ClientRequestId, or TrackingNumber+TrackingCarrier.' This tells the agent exactly how to invoke the tool, though it doesn't explicitly compare with alternatives like purchase_label or track. The context is clear enough for correct usage.

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