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

With no annotations, the description carries the full burden, and it does add real value: it discloses the mod-97 check, the four-character rotation, and the normalization applied (upper-casing, space removal), plus the shape of the result. It does not state what happens on failure (error vs. valid:false), nor does it flag that the single input parameter is technically optional per the schema.

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 and dense: the algorithm and return shape come in one sentence, with the trial-call note as a separate short clause. Minor waste in the 'Validate IBAN: Validate an IBAN' echo of the name, but nothing that meaningfully dilutes the signal.

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 single-input, no-output-schema validator, the description covers the return shape and normalization, which is most of what matters. It leaves open the error path for invalid IBANs and whether the value parameter is required, both of which an agent needs in order to call and handle results correctly.

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?

One parameter with 0% schema description coverage, so the description has to compensate – and it largely does by establishing that the input is an IBAN string and that spaces/case are tolerated and normalized. It stops short of naming the 'value' parameter or giving a concrete example, which is the only remaining ambiguity.

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 and resource (validate an IBAN) and even names the underlying algorithm (mod-97), so the operation is unambiguous. However, it never distinguishes itself from close siblings in the catalog such as x402-iban-validate and x402-is-iban, so an agent scanning siblings still has to guess which one to pick.

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?

Usage is only implied by the verb 'validate' – there is no explicit statement of when to choose this over x402-is-iban or x402-iban-validate, and no mention of preconditions or edge cases (e.g. too-short input, non-IBAN characters). The agent gets a reasonable default context but no routing guidance.

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