validate_ibans

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

With no annotations, the description carries the full burden and does so well: it discloses auth requirements (key optional), rate limits (10 per call, daily per-IP allowance), the difference in returned data between free and paid tiers, and the critical caveat that a valid result does not prove an account exists.

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?

Four tight sentences, front-loaded with the core purpose, then limits, then tier differences, then the honest caveat. Every sentence adds distinct information with no redundancy.

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?

Output schema exists, so return structure need not be restated; the description still usefully previews what paid plans return. Tiering, limits, and the account-existence caveat cover everything an agent needs to invoke and interpret this 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?

One parameter (ibans array) with 0% schema coverage, so the schema adds nothing. The description implies batching of multiple IBAN strings and adds a meaningful constraint (max 10 per call), but does not describe the expected string format per element.

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) and resource (IBANs) and enumerates exactly what is checked: country format, length, MOD-97 checksum. This cleanly separates it from the sibling generate_test_ibans (creates rather than checks) without needing to name it.

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 operating conditions: works without an API key up to 10 IBANs per call, and setting IBANGEN_API_KEY unlocks bank/BIC/reachability data. It does not explicitly say when to prefer this over lookup_bank, so it stops short of full alternative routing.

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