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

With no annotations, the description carries full responsibility for behavior disclosure. It thoroughly explains failure modes (mask violations vs checksum failures), the meaning of 'valid: true' (only check digits, not account existence), and the distinction between country currency and account currency. It also discloses the cross-check logic and what happens in different country registry scenarios. This is comprehensive and leaves no ambiguity.

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 long but well-organized into distinct paragraphs: purpose, cross-check logic, failure mode clarification, semantic limitations, and currency caveat. It front-loads the core purpose and then layers nuances. While some redundancy exists (e.g., repeating 'not the account's denomination'), each sentence contributes essential context. The examples at the end are useful and not extraneous.

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?

Given the tool's complexity, the description covers all critical aspects: validation steps, cross-institution resolution, failure interpretation, output semantics, and currency misconceptions. It references output fields (format_violations, verification_note, currency_note) that likely appear in the output schema, but the description itself provides enough context for an agent to know what to expect. Nothing essential is missing for correct invocation and interpretation.

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 (0% coverage), so the description must compensate. It does so with two examples showing both a bare string and a string with spaces, implying formatting tolerance. However, it doesn't explicitly state allowed characters, length limits, or whitespace handling. The examples are helpful but not exhaustive. A slight gap, but the single parameter is simple enough that the examples suffice.

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's purpose: 'Validate an IBAN and identify the institution that holds the account.' It specifies the exact resource (IBAN) and the verification actions (format, length, mod-97). It distinguishes itself from siblings by explaining its unique cross-check of the beneficiary bank, which no other sibling mentions. This is a specific verb+resource with clear differentiation.

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 provides explicit when-to-use guidance: 'Call this whenever the user supplies an IBAN AND names a beneficiary bank or BIC' and explains why (mismatch detection). It also gives when-not-to-use warnings, such as 'Never rule out the account details on the strength of it when diagnosing a failed payment' and cautions against inferring currency mismatches. While it doesn't name alternative tools directly, the conditions and exclusions are unambiguous and actionable.

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