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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the burden is low. The description adds real value beyond them by disclosing the scope limitation that validity is structural only, and by noting the two output formats returned.

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 with zero filler; the checks are front-loaded and the important caveat about what validity means is placed last as a scope note. 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?

With no output schema, the description usefully explains what is returned (electronic and printed formats) and what the result does not guarantee. The only gap is input-format expectations for the iban argument, which neither the schema nor the description covers.

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 0% for the single 'iban' parameter, so the description must compensate. It implies the parameter is an IBAN string but says nothing about accepted input format (spaces, hyphens, lowercase, country prefix), which is the main ambiguity a caller would face.

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 precise verb ('validates') and resource ('IBAN') and enumerates the exact checks performed: country, country-specific length, and mod-97 check digits. The resource is unambiguous against siblings like validate_email/validate_phone, and the closing clause pins down what 'valid' means.

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?

Gives clear context by defining the semantics of a positive result ('correctly formed; does not confirm the account exists'), which tells an agent when the tool's answer is and isn't sufficient. It names no alternative tools or explicit when-not conditions, but no sibling performs IBAN validation, so there is little routing ambiguity.

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