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

Annotations already mark the tool read-only, idempotent, non-destructive, and open-world, so the bar is lower. The description adds valuable context beyond annotations: offline processing, no data leaving the server, pricing, returned fields, typo check-digit feedback, and BIC-vs-IBAN country matching.

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 core action is front-loaded, and the dense sentence is information-rich without filler. Pricing and HTTPS endpoint notes are relevant operational context for this paid x402 tool.

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 two-parameter, read-only validator with no output schema, the description covers offline behavior, return fields, national check-digit handling, optional BIC validation, and privacy. An agent has enough context to invoke it correctly.

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?

Schema description coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema. It explains that the optional bic parameter triggers ISO 9362 structure checking and BIC-vs-IBAN country matching, which is substantive parameter-level semantics.

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, 'IBAN', then enumerates offline checksum, per-country BBAN structure, national check digits, and optional BIC checks. The resource and scope are unambiguous and distinguishable from sibling validators such as eu_vat_validate or email_validate.

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 implies usage for IBAN validation and explains that the optional BIC check can be used alone, but it gives no explicit when-to-use/when-not guidance and names no alternative sibling tool. Usage is therefore inferable but not fully guided.

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