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

No annotations are provided, so the description carries the full burden. It discloses the validation method (Luhn), which signals a pure format check rather than a live card authorization, and implies a boolean outcome. It does not state whether the input must be digits-only, whether spaces/dashes are stripped, or what a failure looks like, so the burden is only partly met.

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?

A single compact sentence, verb and algorithm front-loaded, with no filler.

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?

Adequate but minimal for a one-parameter validator with no annotations and no output schema. It omits expected input formats and result shape, which a self-contained definition should state given nothing else carries that information.

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 100%, so the baseline is 3. The description does imply the expected value is a card number, but it adds no format, normalization, or length constraints beyond what the schema already says.

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 resource (credit card number) plus the exact algorithm (Luhn). An agent can distinguish this from siblings like x402-credit-card-type or x402-mask-card without opening the schema.

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 guidance on when to use this validator instead of near-identical siblings (x402-credit-card-validate, x402-is-credit-card, x402-is-credit-card-valid, x402-validate-credit-card). The description leaves the agent guessing in a heavily overlapping tool family.

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