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

Goes well beyond the readOnly/openWorld annotations: discloses the external dependency on OpenIBAN's directory, that results may be missing for some banks, the checksum-vs-account-existence limitation, the $0.001 USDC cost via x402 on three chains, and that failed calls are not charged. This is exactly the billing and reliability context an agent needs before calling a paid endpoint.

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?

Three sentences with no filler: validation mechanics first, lookup caveats second, pricing third. Front-loaded and each sentence carries a distinct decision-relevant fact.

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 values need not be explained, and the description supplies the remaining critical context: failure modes, dependency risk, and payment terms. Nothing an agent needs to invoke this correctly is missing.

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 is fully documented in the schema (100% coverage) including the spaces-allowed format and an example, so the description adds little. Baseline 3 applies when the schema does the heavy lifting.

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 and resource chain: validate an IBAN via MOD-97 and country length, then resolve bank name, city and BIC via OpenIBAN. An agent can distinguish this from the many unrelated siblings without opening the schema.

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?

Clearly frames the conditional flow (lookup only happens if checksum passes) and warns that a valid checksum does not prove account existence, which is the key usage caveat. It does not name alternatives, but no sibling tool overlaps this capability, so there is nothing to route away from.

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