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

Annotations already declare readOnlyHint=true and destructiveHint=false; the description adds the 'FREE STATUS' cost signal and the fact that a result hash is returned. It does not contradict annotations, but it also does not reveal auth requirements, rate limits, or error behavior.

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?

Two short clauses with no bloat; 'FREE STATUS' is front-loaded and the main sentence concisely states input and output. The standalone 'FREE STATUS' is somewhat redundant, preventing a 5.

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 one-parameter, read-only tool, the description covers the essential input and output. However, with no output schema, it leaves the shape or possible values of 'fulfillment state' and 'result hash' unspecified, and it does not clarify the relationship to similarly named siblings.

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?

The schema provides only the parameter name and length constraints, with 0% description coverage. The description clarifies that the parameter is a purchase idempotency key, adding domain meaning, but it does not explain where the key comes from or expected format beyond min/max length.

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 names a specific resource ('fulfillment state and result hash') and a clear lookup key ('purchase idempotency key'), so an agent knows what the tool returns. It does not explicitly distinguish this from sibling tools like fulfillment.get or get_fulfillment_status, so it stops short of a 5.

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 phrase 'by purchase idempotency key' implies the tool should be used when an agent has that key and needs fulfillment status. It gives no explicit guidance on when to prefer this over siblings or any exclusion criteria.

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