Identifier check digits: IBAN, ISBN, GTIN, VIN, ISIN, LEI and more, in a batch

$0.005 USDC per call · Business, finance and compliance · POST /api/v1/checksum · Id checksum

Validates the format and check digit of up to 100 identifiers per call, for an agent about to put an IBAN, ISBN, GTIN/EAN/UPC, container number, VIN, ISIN, CUSIP, SEDOL, LEI, IMO number, BIC or Luhn number into a payment, order or record. Each item is {kind, value}; with kind omitted the engine proposes candidate kinds and answers unknown if two kinds both validate. Reports the normalized form (lower case and spaces accepted) and the expected vs actual check digit. It does not check that the identifier exists, is registered or belongs to anyone, and it does not apply national BBAN check digits inside an IBAN.

What you get

A wrong digit in an IBAN or ISIN costs a bounced payment or a misrouted trade; one call checks a whole batch.

Call it

Send the JSON body below to https://agents.writerslogic.com/api/v1/checksum. An unpaid request answers 402 with the price and how to pay; a request that fails with a 5xx status is not charged.

curl -i -X POST https://agents.writerslogic.com/api/v1/checksum \
  -H 'content-type: application/json' \
  -d '{"items":[{"kind":"iban","value":"gb82 west 1234 5698 7654 32"},{"value":"978-0-306-40615-7"},{"kind":"vin","value":"1G4AH59H45G118341"}]}'

Input

Field	Type	Required	Description
`items`	array<object>; max 100 items	yes

Example request body

{
  "items": [
    {
      "kind": "iban",
      "value": "gb82 west 1234 5698 7654 32"
    },
    {
      "value": "978-0-306-40615-7"
    },
    {
      "kind": "vin",
      "value": "1G4AH59H45G118341"
    }
  ]
}

Result

The response is { "data": ..., "_provenance": ... }. data carries these fields; _provenance is a signed W3C Verifiable Credential with a C2PA-style manifest, checked free at POST /api/v1/verify-provenance.

Field	Type	Required	Description
`status`	string; one of "pass", "fail", "unknown", "unsupported"	no	pass: every rule held. fail: a rule was violated (see witnesses). unknown: the input lacks the evidence to decide. unsupported: outside what this engine covers. Missing evidence is never a pass.
`results`	array<object>	no
`counts`	object	no	Items per status.
`witnesses`	array<object>	no
`versions`	object	no	Every semantic dependency of this answer (engine, tables and their as-of dates, tokenizer, calendar, rounding profile).
`limits`	array<string>	no
`deterministic`	boolean	no	Always true: pure code, no model.

Pay and connect

Available through: x402 (USDC on Base), MCP. MCP clients reach it through the identifier-text-kit package.

Machine-readable

This agent as JSON (schemas, example, OpenAPI operation)
Free signed sample response
OpenAPI 3.1 · Catalog · Index of every agent