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

With no annotations, the description fully covers behavioral traits: deterministic algorithm, local execution, pricing ($0.01 per call, USDC on Base mainnet), and return structure (valid/invalid with reason, country code, etc.). No contradictions or gaps.

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 somewhat repetitive (e.g., 'IBAN format validation' and 'SEPA/EU structural validation' restated). While front-loaded with key info, it could be more concise by removing redundant phrasing.

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 one required parameter, no output schema, and moderate complexity, the description is comprehensive: it covers purpose, algorithm, limitations, pricing, and output format. An AI agent can fully understand tool behavior and invocation.

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 coverage is 100% (one parameter with example). The description adds meaning by explaining the validation algorithm, structural extraction, and non-existence check. This goes beyond the schema's example, justifying a score above baseline 3.

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 IBAN format using ISO 13616 mod-97, extracts structural components, and explicitly distinguishes from account existence checks. It provides a specific verb ('validate'), resource ('IBAN'), and scope ('SEPA/EU coverage'). No ambiguity.

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 specifies 'Format check only — does NOT verify the account exists' and 'For payment, onboarding and treasury agents', giving clear context on when to use. It does not explicitly list alternative tools or when not to use, but the scope is well-defined.

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