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

With no annotations, the description carries the burden and discloses meaningful behavior: it is free, offline, uses no outside source, and performs specific validation checks. It does not describe return structure or invalid-IBAN behavior, but the core operational traits are transparent.

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 a single efficient statement with the key validation behavior front-loaded. The word 'FREE' is brief and contextually useful, and there is no unnecessary text.

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 simple one-parameter validator with no output schema, the description covers the validation logic and some returned data. However, it does not explain the shape of the validation result, how invalid IBANs are reported, or accepted input formats, leaving some gaps an agent may need to infer.

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 schema has only one parameter with 0% description coverage, so the description should compensate. It does not specify accepted input formatting, such as whether spaces or lowercase letters are allowed, and adds little beyond the self-evident parameter name 'iban'.

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?

The description gives a specific verb and resource: validate an IBAN. It also names the exact checks performed (country, length, ISO 13616 mod-97 checksum) and extra outputs (bank code, formatted IBAN), making the tool unambiguous and distinct from unrelated 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?

The description establishes a clear usage context: offline validation that is free and requires no outside source. It does not explicitly state when not to use the tool, but there are no similar sibling alternatives that would require routing guidance.

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