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

With no annotations, the description carries the full burden; it does disclose the validation method (format + mod-97) and the response content (validity, country code), which is genuinely useful. It omits auth/payment mechanics beyond a terse '5 free trial calls per signed wallet', and says nothing about 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?

One compact, front-loaded sentence that leads with the action and method. The trailing trial-call/pricing emoji fragment is slightly noisy but does not bury the core meaning.

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?

No output schema exists, and the description compensates by naming the returned fields (validity, country code), which is helpful. But with 0% parameter coverage and two ambiguous inputs, an agent still lacks enough to call the tool confidently.

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 0% with two undocumented parameters ('iban' and 'input') and none required. The description implies an IBAN is the subject, which loosely maps to 'iban', but it never explains the relationship between 'iban' and 'input' or which one to supply, leaving the caller guessing.

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+resource ('Validates an IBAN') and goes further to name the mechanism ('format and mod-97 checksum rules') and the return values ('validity plus the country code'). However, it does not differentiate from siblings like x402-validate-iban and x402-is-iban, which appear to do nearly the same thing.

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?

There is no guidance on when to use this tool versus x402-validate-iban or x402-is-iban, no prerequisites, and no exclusions. The only conditional element is a trial/pricing note, which is not selection guidance.

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