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

With no annotations, the description carries the full behavioral burden. It usefully discloses the cost ($0.01 USDC on Base via x402), which is real operational context an agent needs before calling. It still omits rate limits, error behavior for malformed GTINs, and whether validation is strictly read-only with no side effects.

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 tight sentences, front-loaded with what the tool does, then the cost. No filler, no redundancy, every clause earns its place.

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, no-annotation, no-output-schema tool, the description covers purpose, formats, and price. It leaves gaps around failure modes (invalid or non-compliant GTINs), response shape, and whether results distinguish valid formats from check-digit failures. The payment handshake itself is already in the schema.

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 50%. The description adds genuine meaning for gtins by enumerating accepted identifier formats (GTIN-8/12/13/14, check digits), which the schema's generic string/number union does not convey; the 1-100 range merely restates minItems/maxItems. payment_signature is fully documented in the schema, so the description does not need to cover it.

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), the resource (GTIN identifiers), the supported formats (GTIN-8/12/13/14), and the batch scope (1-100). The batch scope implicitly separates it from single_gtin_check, but it never names the sibling, so differentiation is inferential rather than explicit.

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 1-100 range implies batch usage versus a single-item tool, and the pricing sentence tells the agent a cost is involved. However, it never states when to choose this over single_gtin_check or the other catalog siblings, nor any exclusions or prerequisites.

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