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

Goes well past the annotations (readOnlyHint, openWorldHint) by disclosing price ($0.001 USDC per call via x402), the unpaid-call failure mode (returns x402 payment requirements), and the exact retry mechanisms (X-PAYMENT or PAYMENT-SIGNATURE header, or params._meta["x402/payment"]). That is exactly the operational context an agent needs before calling. It does not describe the shape of the successful paid response, which keeps it off a 5.

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?

Front-loaded with purpose, then the negative scope, then the payment mechanics in the order an agent will encounter them. Every sentence carries information: capability, boundary, cost, and recovery path. No filler or repetition of the title.

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 one-parameter tool with no output schema, the description covers cost, auth flow, failure recovery, and the semantic limits of the check. The remaining gap is the return format of a successful paid call (per-code verdicts versus a single aggregate), which matters for a batch tool but is not stated anywhere.

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?

With 100% schema coverage and a single parameter, the schema already documents the accepted formats, the regex pattern, the 1-100 item bound, and the leading-zero preservation. The description largely restates those constraints rather than adding new meaning such as batching behavior or how mixed-validity inputs are handled, so baseline 3 applies.

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?

States a specific verb (validate) and a specific resource (GTIN-8/12/13/14 check digits), plus the scope qualifier 'for product catalogs, preserving leading zeros.' Sibling tools such as product_compliance_checklist or company_legal_identifier are clearly different resources, so an agent can route correctly from the first sentence alone.

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?

"No registry, ownership or authenticity verification" is an explicit when-not boundary that prevents misuse as a product-authenticity check. What is missing is a named alternative for that adjacent need, so the exclusion tells the agent what this is not without telling it where to go instead.

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