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

The description adds significant behavioral context beyond annotations: the paid nature (300 micro-dollar credits per successful call), the prerequisite of preparation, the authorization requirement, and the fact that a new requestId creates a new billable operation. This aligns with idempotentHint=true and readOnlyHint=false without contradiction.

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 and front-loaded: the core purpose appears first, followed by essential billing and prerequisite information. Every sentence conveys necessary operational detail, with no filler or repetition of schema content.

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 paid, prerequisite-gated tool, the description covers the critical operational context: cost, preparation requirement, authorization, recovery behavior, and billing semantics. Since an output schema exists, the lack of return-value explanation is not a gap.

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 67%, with requestId and maxPriceMicroUsd already documented in the schema. The description adds general meaning by clarifying that the code parameter is a GTIN check-digit validation, but it does not elaborate on the input object structure or code format beyond what the schema provides.

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 and resource: validating check digits for GTIN-8, UPC/GTIN-12, EAN/GTIN-13, and GTIN-14. It also explicitly distinguishes the tool from product lookup, which differentiates it from sibling tools like commerce_offer_extract.

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 explicit prerequisites and workflow context: use agent_utilities_prepare first, require existing credits and a private Authorization header, and reuse prepared arguments for recovery. It clearly explains the billing implications but does not name an alternative for product lookup beyond saying 'no product lookup.'

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