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

With no annotations, the description carries the full burden. It discloses the credit cost and API key requirement, but does not describe the return format, potential side effects, or whether the tool is read-only, which are relevant for a validation tool.

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 concise sentence that front-loads the primary action ('Validate an IBAN') and includes useful extra context (credits, API key) without unnecessary words.

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?

The description covers purpose, cost, and auth, which is a good start, but lacks a description of the return value since there is no output schema, and does not explicitly guide the agent on when to choose this over sibling validation tools.

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 provides no description for the 'iban' parameter, and the description only notes that it validates an IBAN and mentions ISO 13616. It offers minimal added meaning beyond the parameter name and length constraints, providing no format examples or additional guidance.

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 clearly states the tool validates an IBAN, specifies the ISO 13616 check digit standard, and mentions SEPA membership, which distinguishes it from sibling validation tools like validate_email and validate_vatid.

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?

It clearly indicates this is for IBAN validation and notes that it costs 2 credits and requires an API key, providing usage prerequisites. However, it does not explicitly mention when not to use it or name alternative tools for other entity types.

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