Format validation only (no VIES lookup) for an EU VAT number: checks the 2-letter member-state prefix (EL for Greece, XI for Northern Ireland) against that country's digit/letter pattern. A format-valid result does not mean the number is actually registered.
| Name | Required | Description | Default |
|---|---|---|---|
| value | Yes | identifier or value to check |
| Name | Required | Description | Default |
|---|---|---|---|
| valid | Yes | ||
| reason | No |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It discloses that the tool only validates format, not real registration, explaining the logic (prefix check, pattern). It does not mention side effects, idempotency, or error behavior, but for a simple validation tool this is adequate.
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?
Two sentences, no redundant information. The key point 'Format validation only' is front-loaded, and every sentence adds value. Highly efficient.
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 simplicity (1 required parameter, no annotations, output schema exists), the description is complete. It explains what the tool does, its limitations, and the format rules. The agent can correctly determine when to invoke it.
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% with a generic description 'identifier or value to check'. The description adds significant value by specifying the value is an EU VAT number, explaining the format rules (prefix, pattern), and clarifying limitations. This enriches the parameter semantics beyond the schema.
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 does format validation of EU VAT numbers, specifying it checks the 2-letter prefix and digit/letter pattern. It distinguishes itself from siblings (EAN, IBAN, ISBN, etc.) by focusing on VAT numbers and explicitly mentioning 'no VIES lookup'.
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 guidance: 'Format validation only (no VIES lookup)' and warns that a format-valid result does not mean registration. This helps the agent decide when to use this tool versus a registration lookup. It does not directly compare to sibling tools, but the different types are clear from names.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.
Each tool validates a completely distinct type of identifier (barcodes, IBANs, ISBNs, Luhn-based numbers, SWIFT/BIC codes, and EU VAT numbers). There is no overlap in purpose, and descriptions clearly differentiate the specific format and algorithm used.
All six tools follow an identical naming pattern: the lowercase identifier name followed by '_validate'. This consistent noun_verb structure makes it easy for an agent to predict the tool name for any identifier type.
With six tools covering the most common checksum-based identifiers (barcodes, IBANs, ISBNs, payment cards, SWIFT/BIC, EU VAT), the server is well-scoped. Each tool serves a clear purpose without unnecessary redundancy or excessive complexity.
The tool set covers the major standardized identifiers that rely on checksums or structural validation. While additional identifiers like VIN or SSN could be added, the current selection represents a natural and comprehensive set for a 'Checksum Validator' server.