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

With no annotations, the description carries the full behavioral burden. It explains how the tool differs from mod-97-only validators, that it checks BBAN structure, that corrected check digits are suggested, and that bankName can be null. A slight internal inconsistency exists between 'bank and branch codes' and the later explanation only mentioning bankName, but overall behavior is well disclosed.

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?

The description is concise and front-loaded with the core action. Each subsequent sentence adds meaningful information — why stronger validation matters, correction behavior, bank-name limitations, and what the tool is not. No wasted words or repetition.

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?

Given that there is no output schema, the description compensates by explaining corrective suggestions, null bankName values, and country-specific resolution. It could be more explicit about the exact return fields, but the key behavioral context is present and sufficient for an agent to select and interpret the tool.

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?

Both parameters (iban and expectCountry) are fully described in the input schema, so the description's lack of extra parameter-level detail is acceptable. It adds no new semantic or syntax information beyond schema coverage, earning the baseline 3.

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?

Opening sentence clearly states the tool's purpose: 'Validates an IBAN from any of 70+ countries: checksum, country length and in-country account structure, and resolves the bank and branch codes.' This names a specific verb, resource, and scope, distinguishing it from the many sibling validation tools by focusing exclusively on IBANs.

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?

The description gives clear context about when this tool exceeds basic checksum validation and warns against interpreting it as a SWIFT directory. It does not explicitly name alternative tools or state 'when not to use', but the limitations and unique added value are clearly implied.

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