Tanod MCP server

utilpeek: check the format and check digits of an IBAN, VAT, ISBN or other ID

validate_identifier

Read-onlyIdempotent

Checks the format and check digits of identifiers like IBANs, VAT numbers, ISBNs, and national IDs offline, returning validity, failure reasons, and formatted values.

Instructions

utilpeek: check the format and check digits of an identifier. For a VIN's vehicle use decode_vin; for phone numbers use parse_phone_number. Returns valid, reason (invalid_checksum, invalid_length, invalid_format, ... when not valid), compact, formatted and a kind-specific detail (an IBAN's country and bank code, an ISBN's ISBN-10/13 forms, ...). An invalid identifier is a normal answer (charged); a malformed request is a 422 (not charged). Checks format and check digits only, offline (python-stdnum): a valid result does not mean the identifier exists or is registered (no registry, bank or VIES call). Payment card numbers are not accepted, not even under luhn. The submitted value is processed in memory only, never logged or stored. Typically under 0.1 s. Price: USD 0.001. Free: 10 utilpeek calls per IP per UTC day. Docs: https://tanod.dev/learn/iban-validation-api.html

Input Schema

TableJSON Schema

Name	Required	Description	Default
`kind`	Yes	Identifier kind: iban, bic, vat (EU, format only, no VIES), isbn, issn, ean, isin, lei, imo, luhn (generic mod-10), or a national format (au_abn, br_cnpj, br_cpf, ca_bn, ch_uid, de_idnr, es_nif, fr_siren, fr_siret, gb_vat, in_pan, mx_rfc, nl_bsn, us_ein). No payment card numbers.
`value`	Yes	The identifier (1-64 printable ASCII characters).

Output Schema

TableJSON Schema

Name	Required	Description
`kind`	No
`note`	No
`error`	No	Only on an error result: an object {code, message}, or the reason string of an x402 PaymentRequired object.
`label`	No
`valid`	No
`detail`	No
`reason`	No
`source`	No
`compact`	No
`formatted`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.0Oct 15, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Goes well past the annotations (readOnly/idempotent/non-destructive) with charging semantics (invalid identifier is a normal, charged answer; malformed request is a 422, not charged), offline python-stdnum execution with no registry/bank/VIES call, in-memory-only handling with no logging, latency (~0.1 s), price, and free-tier quota. These are exactly the operational facts an agent needs for cost and privacy decisions.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Dense but front-loaded: purpose, then sibling routing, then return shape, then operational behavior. Every clause carries non-redundant information, and no sentence merely restates the tool name or annotations.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, return values need not be enumerated, yet the description still names the key fields and error reasons. Combined with pricing, error-code semantics and the offline caveat, nothing an agent needs to call this correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description still adds real meaning: it constrains the `luhn` kind (no payment card numbers) beyond the schema's 'generic mod-10' wording and illustrates what the kind-specific `detail` field carries. The `value` length/character constraints remain schema-only, which keeps this from a 5.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource ('check the format and check digits of an identifier') and immediately routes two adjacent cases to named siblings (decode_vin for VINs, parse_phone_number for phone numbers). An agent can distinguish this from lookup_lei/search_lei and validate_json without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit alternatives and when-not conditions are given: VINs go to decode_vin, phones to parse_phone_number, and 'Payment card numbers are not accepted, not even under `luhn`' rules out a tempting misuse. It also states the scope boundary (format/checksum only, no registry or VIES lookup), which tells the agent when this tool is insufficient.

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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