validate_ibanValidates an IBAN offline: country-specific length and ISO 7064 mod-97 checksum, for 60+ countries. Returns valid true/false with the country and, when invalid, an actionable reason. This checks structure, not account existence. Light read: costs 0.2 credit.
| Name | Required | Description | Default |
|---|---|---|---|
| iban | Yes | IBAN to validate, spaces allowed, e.g. 'DE89 3704 0044 0532 0130 00' |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden and does so well: it discloses the operation is fully offline, the precise validation rules applied, coverage scope, the return shape (valid true/false, country, actionable reason when invalid), the key limitation (structure only, not account existence), and even the cost (0.2 credit). These are exactly the traits an agent cannot infer from the schema.
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?
Three short sentences, tightly front-loaded: capability first, return contract second, limitation and cost last. No filler and no restatement of the tool name or title.
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?
No output schema exists, yet the description fully specifies the return contract (boolean valid, country, reason on failure), the semantic limitation, and the cost. For a single-parameter, offline validation tool this leaves nothing material unstated.
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% and the single parameter already documents that spaces are allowed with a worked example, so the baseline is 3. The description adds nothing about parameter format, normalization, or casing beyond what the schema states.
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) and goes further by naming the exact mechanisms: country-specific length rules and the ISO 7064 mod-97 checksum, plus the 60+ country coverage. An agent can distinguish this from every sibling (verify_vat, verify_company, screen_sanctions) without opening a schema.
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?
Provides a clear usage boundary: 'This checks structure, not account existence,' which prevents the agent from over-trusting a positive result. It does not name an alternative tool or state prerequisites, but none of the siblings overlap with IBAN validation, so the context is sufficient without an explicit routing statement.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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