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

The description adds valuable behavioral context beyond the annotations: the URL expires within minutes, re-calling fetches a fresh URL, and the call only works after label_ready. This complements the readOnlyHint and idempotentHint annotations by explaining real-world side effects and constraints.

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?

Three short sentences with no filler. The main action is front-loaded, followed by the expiry/freshness caveat and the state requirement. Every sentence adds necessary information.

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 read-only tool with one well-documented parameter and no output schema, the description covers the essential behavior, state precondition, and URL freshness semantics. The annotations already establish idempotence and non-destructiveness, so nothing critical is missing.

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% and the single parameter return_id is already well described in the schema. The tool description does not add parameter-specific detail, relying instead on the schema's documentation. This matches the baseline for high schema coverage.

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 ('Fetch') and resource ('short-lived signed URL for the return shipping label PDF'), making the tool's function immediately clear. This clearly differentiates it from sibling tools like returns_get and returns_list, which return return data rather than a label URL.

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 clearly states when the tool can be used: 'Only available once the return has progressed to label_ready.' It also explains the re-call behavior for expired URLs. However, it does not explicitly mention alternatives or when not to use it, so it falls slightly short of full guidance.

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