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

With no annotations, the description fully describes the tool's behavior: it validates specific criteria and does not perform other operations. It implicitly communicates non-destructive nature via 'validates'. Could be more explicit about side effects (none), but adequate.

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 sentences, front-loaded with action. No redundant or vague language. Every word contributes to clarity. Second sentence efficiently states exclusions. Perfectly sized.

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 the presence of an output schema (not shown), the description need not detail return values. It covers the validation logic (length and checksum) and explicitly states what is not done. For a simple validation tool with one input, this is complete and sufficient.

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?

The single parameter 'value' has a generic schema description ('identifier or value to check'). The tool description adds essential meaning by specifying that the value is an IBAN string, and that validation checks length and checksum. This compensates for the schema's lack of specificity.

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?

Clearly states the tool validates an IBAN's length and mod-97 checksum, and explicitly distinguishes from decomposition and BIC resolution. Differentiates from sibling tools like ean_validate, isbn_validate, and swiftbic_validate by specifying IBAN-specific validation.

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?

Provides clear context: validates length and checksum, but does not decompose or resolve BIC. This implies when to use (when IBAN format validation is needed) and when not (when further decomposition is needed). Lacks explicit naming of alternatives but is sufficient for decision-making.

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