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

With no annotations, the description carries the full burden. It usefully discloses the validation steps, that a pretty-printed grouping is returned when valid, and the per-call x402 price/payment chain. However, it never states what happens on invalid input (error vs. boolean), so a mutation-free-read tool's failure behavior remains opaque.

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 dense clause describing what is checked followed by return-value and pricing notes; the core purpose is front-loaded and no sentence is wasted. The em-dash price suffix is slightly awkward but compact.

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 validator with no annotations and no output schema, the description covers the validation semantics, the valid-case return value, and the payment requirement. It is only short of the invalid-case response shape, which for a boolean-style validator is a minor omission.

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% and the single 'iban' parameter is already documented, including that spaces are ignored. The description adds no syntax, format, or normalization detail beyond what the schema provides, so the 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) plus the exact resource (International Bank Account Number) and enumerates the checks performed: country code, country-specific length, and ISO 7064 MOD 97-10 check digits. This is unambiguous and clearly distinct from the calculator/converter siblings.

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 implied — you validate an IBAN before relying on it — but there is no explicit when-to-use, when-not-to-use, or alternative named (the nearest analog, dev_email_validator, is not referenced, though it is a different domain so that is forgivable). Adequate but with a clear gap.

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