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

The annotations already declare read-only, idempotent, open-world, and non-destructive behavior, so the description does not need to repeat safety basics. It adds useful behavioral detail: ISO 13616 validation, MOD-97 checksum checking, country/jurisdiction matching, fraud-prevention intent, and per-call pricing after a free tier.

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 three tight sentences and front-loads what is validated before explaining the fraud-prevention purpose and price. The pricing parenthetical is useful but slightly ancillary to the core capability statement.

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 four-parameter read-only validation tool with annotations, full schema coverage, and an output schema, the description gives enough context to understand purpose and behavior. The main omission is explicit routing against sibling tools, which is handled separately in usage guidelines.

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 schema already documents all four parameters and the baseline is 3. The description clarifies that the country match is against expected corporate jurisdiction, but it adds little beyond the schema for payeeName and payeeTaxId.

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 uses specific verbs (validates, verifies) and names the resource (IBAN, issuing country, corporate jurisdiction), plus ISO 13616 and MOD-97. It does not explicitly distinguish this tool from siblings such as verify_eu_vat or check_vendor, so it stops short of a 5.

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 implies the tool should be used before payments to prevent invoice fraud and redirection attacks, which gives contextual when-to-use guidance. However, it does not state when not to use it or name the sibling alternatives for overlapping vendor/tax-country checks.

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