# Duo Data Utilities

> IBAN, ISIN, VAT & tax ID, barcode, timezone and geo APIs: 33 independent pay-per-call HTTP GET endpoints. $0.05 flat per call, paid over x402 (HTTP 402 + USDC on Base, eip155:8453). No account, no API key, no subscription. Operated by Duo Leads, hello@duoleads.com.

How to pay: Every route is paid per call over x402 v2: HTTP 402 plus USDC on Base (CAIP-2 eip155:8453). An unpaid request returns 402 with a base64 `PAYMENT-REQUIRED` header describing the price. Sign an EIP-3009 authorization for that amount and retry the same request with a base64 `PAYMENT-SIGNATURE` header; the 200 response carries a base64 `PAYMENT-RESPONSE` settlement receipt. Requests that are malformed (400), unknown (404), sent with the wrong method (405) or too large (413) are rejected before the paywall and are never charged.

Every 200 response is {ok, route, version, data, meta}; errors are {ok:false, error:{code, param, message, expected}}. Deterministic routes are cacheable.

## Machine-readable

- [OpenAPI 3.1](https://api.duoleads.com/openapi.json): full schema for every endpoint
- [Agent skill](https://api.duoleads.com/skill.md): which route for which need, with the price
- [Catalogue manifest](https://api.duoleads.com/v1/manifest): every route, parameter and example as JSON (free)
- [A2A agent card](https://api.duoleads.com/.well-known/agent-card.json): skills and the a2a-x402 extension
- [A2A endpoint](https://api.duoleads.com/a2a): JSON-RPC (SendMessage / message/send); skill execution is paid via a2a-x402
- [x402 resource index](https://api.duoleads.com/.well-known/x402): every paid resource URL
- [MCP endpoint](https://api.duoleads.com/mcp): Streamable HTTP; tools/list is free, tools/call is paid
- [npm: duo-data-utilities](https://www.npmjs.com/package/duo-data-utilities): TypeScript client
- [GitHub: hiesem/duo-data-utilities](https://github.com/hiesem/duo-data-utilities): TS + Python clients, MCP configs, examples

## Legal

- [Documentation](https://api.duoleads.com/docs): parameters, output, sources and licences per route
- [Terms](https://api.duoleads.com/terms) ([JSON](https://api.duoleads.com/terms.json)) and [privacy](https://api.duoleads.com/privacy)

## Identifiers and check digits (id)

- [/v1/id/national](https://api.duoleads.com/v1/id/national?country=NL&kind=bsn&value=111222333): VAT, tax ID and national ID validator: 23 countries, checksum only (VAT formats BE, DE, FR, IT, PL, AT, CH, IE). $0.05/call.
- [/v1/id/gs1](https://api.duoleads.com/v1/id/gs1?value=5901234123457): GTIN barcode validator: EAN-13, UPC-A (GTIN-12), GTIN-8/14, GLN and SSCC check digits. $0.05/call.
- [/v1/id/security](https://api.duoleads.com/v1/id/security?value=US0378331005): ISIN validator plus CUSIP, SEDOL and FIGI check-digit validation; builds an ISIN from an NSIN. $0.05/call.
- [/v1/id/iban](https://api.duoleads.com/v1/id/iban?iban=NL91+ABNA+0417+1643+00): IBAN validator: length, mod-97 check digits, bank/branch/account breakdown (89 countries). $0.05/call.
- [/v1/id/iban-build](https://api.duoleads.com/v1/id/iban-build?country=NL&bank=ABNA&account=0417164300): IBAN generator: build an IBAN from country and BBAN or bank/branch/account, computing check digits. $0.05/call.

## Dates, times and zones (time)

- [/v1/time/zone](https://api.duoleads.com/v1/time/zone?zone=Europe%2FAmsterdam&instant=2026-10-25T00%3A30%3A00Z): Timezone converter: instant to local time in an IANA time zone and back, with UTC offset and DST state. $0.05/call.
- [/v1/time/dst](https://api.duoleads.com/v1/time/dst?zone=Europe%2FAmsterdam&from=2026-01-01&years=1): DST transitions: next daylight-saving time changes for an IANA time zone. $0.05/call.
- [/v1/time/business-days](https://api.duoleads.com/v1/time/business-days?from=2026-12-24&days=5&holidays=2026-12-25%2C2026-12-26%2C2027-01-01): Business days calculator: add or count working days with your weekend mask and holiday list. $0.05/call.
- [/v1/time/rrule](https://api.duoleads.com/v1/time/rrule?rrule=FREQ%3DMONTHLY%3BBYDAY%3D-1FR%3BCOUNT%3D3&dtstart=2026-01-01T09%3A00%3A00&zone=Europe%2FAmsterdam): RRULE expander: RFC 5545 recurrence rule to concrete occurrence dates. $0.05/call.
- [/v1/time/calendar](https://api.duoleads.com/v1/time/calendar?date=2026-09-28&to=islamic%2Chebrew%2Cjapanese): Calendar converter: Gregorian to Hijri, Hebrew, Japanese era, Persian and more, plus Easter date. $0.05/call.

## Text and Unicode (text)

- [/v1/text/slug](https://api.duoleads.com/v1/text/slug?text=Cr%C3%A8me+Br%C3%BBl%C3%A9e+%E2%80%94+%C3%86r%C3%B8sk%C3%B8bing%2C+Stra%C3%9Fe+42&lang=de): Slug generator: Unicode-aware URL slug with transliteration. $0.05/call.
- [/v1/text/transliterate](https://api.duoleads.com/v1/text/transliterate?text=%D0%A9%D1%83%D0%BA%D0%B0&standard=iso-9): Cyrillic transliteration to Latin (ISO 9:1995, BGN/PCGN Russian). $0.05/call.
- [/v1/text/unicode](https://api.duoleads.com/v1/text/unicode?text=caf%C3%A9&form=nfd): Unicode normalization (NFC/NFKC), script detection and homoglyph/confusable check. $0.05/call.
- [/v1/text/similarity](https://api.duoleads.com/v1/text/similarity?a=kitten&b=sitting): String similarity: Levenshtein, Jaro-Winkler distance and Soundex/Metaphone phonetic keys. $0.05/call.

## Encoding, parsing and digests (code)

- [/v1/code/url](https://api.duoleads.com/v1/code/url?url=https%3A%2F%2Fa.b.example.co.uk%3A443%2Fx%2F..%2Fy%3Fq%3D1%26q%3D2%23f): URL parser: parse, canonicalize and extract the registrable domain (eTLD+1). $0.05/call.
- [/v1/code/idn](https://api.duoleads.com/v1/code/idn?domain=b%C3%BCcher.example): Punycode converter: IDN domain to ASCII and back, with IDNA2008 label validation. $0.05/call.
- [/v1/code/semver](https://api.duoleads.com/v1/code/semver?version=1.2.3-rc.1%2Bbuild.5): Semver parser: parse and compare versions, check range satisfaction. $0.05/call.
- [/v1/code/hash](https://api.duoleads.com/v1/code/hash?algo=sha256&data=hello): Hash generator: SHA-256, SHA-512, SHA-3, Keccak-256, BLAKE2 and HMAC digests. $0.05/call.
- [/v1/code/jwt](https://api.duoleads.com/v1/code/jwt?token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c&at=2026-09-28T00%3A00%3A00Z): JWT decoder: header, claims and expiry state (no signature verification). $0.05/call.

## Geodesy and geometry (geo)

- [/v1/geo/geohash](https://api.duoleads.com/v1/geo/geohash?op=encode&lat=52.3728&lon=4.8936&precision=9): Geohash encoder and decoder with neighbour cells. $0.05/call.
- [/v1/geo/pluscode](https://api.duoleads.com/v1/geo/pluscode?lat=52.3728&lon=4.8936): Plus code (Open Location Code) encoder and decoder. $0.05/call.
- [/v1/geo/polygon](https://api.duoleads.com/v1/geo/polygon?geometry=%7B%22type%22%3A%22Polygon%22%2C%22coordinates%22%3A%5B%5B%5B4.85%2C52.35%5D%2C%5B4.95%2C52.35%5D%2C%5B4.95%2C52.40%5D%2C%5B4.85%2C52.40%5D%2C%5B4.85%2C52.35%5D%5D%5D%7D&lat=52.3728&lon=4.8936): Point in polygon check, plus bounding box, centroid and area for GeoJSON. $0.05/call.
- [/v1/geo/distance](https://api.duoleads.com/v1/geo/distance?lat1=52.3728&lon1=4.8936&lat2=40.7128&lon2=-74.0060): Distance calculator: geodesic distance, bearing and destination point on WGS-84. $0.05/call.

## Blockchain primitives (no RPC) (chain)

- [/v1/chain/address](https://api.duoleads.com/v1/chain/address?address=0xd8da6bf26964af9d7eed9e03e53415d37aa96045): Crypto address validator: detect the blockchain and verify the checksum (EVM, Bitcoin, Solana and more). $0.05/call.
- [/v1/chain/selector](https://api.duoleads.com/v1/chain/selector?signature=transfer%28address%2Cuint256%29): Solidity function selector: Keccak-256, 4-byte selector and event topic from a signature. $0.05/call.

## Static reference tables (ref)

- [/v1/ref/nuts](https://api.duoleads.com/v1/ref/nuts?code=NL32B&include=parents%2Ctypology): NUTS region lookup: EU statistical region codes, names and hierarchy. $0.05/call.
- [/v1/ref/airport](https://api.duoleads.com/v1/ref/airport?code=AMS): Airport lookup by IATA or ICAO code: name, coordinates, elevation, time zone; nearest airports. $0.05/call.
- [/v1/ref/currency](https://api.duoleads.com/v1/ref/currency?code=EUR&include=territories): Currency lookup: ISO 4217 codes, names, minor units and cash rounding. $0.05/call.
- [/v1/ref/country](https://api.duoleads.com/v1/ref/country?code=NL): Country lookup: ISO 3166 codes, currency, TLD, UN region and ISO 3166-2 subdivisions. $0.05/call.

## Numbers and money arithmetic (num)

- [/v1/num/radix](https://api.duoleads.com/v1/num/radix?value=0xdeadbeef&to=10): Base converter: integers between number bases 2 to 36 (hex, binary, octal). $0.05/call.
- [/v1/num/words](https://api.duoleads.com/v1/num/words?value=1234&lang=nl): Number to words in 12 languages, with ordinal and currency forms. $0.05/call.
- [/v1/num/stats](https://api.duoleads.com/v1/num/stats?values=1%2C2%2C3%2C4%2C5): Statistics calculator: mean, median, standard deviation, quartiles and percentiles. $0.05/call.
- [/v1/num/allocate](https://api.duoleads.com/v1/num/allocate?amount=100.00&currency=EUR&parts=3): Money split: allocate an amount into shares with no rounding loss. $0.05/call.

## Disclaimer

Factual output of a deterministic computation over public data. Provided as is, with no warranty of accuracy, completeness or availability. Not investment, financial, legal, tax, medical or any other professional advice, and not a recommendation. Verify before relying on it. Terms: https://api.duoleads.com/terms

## Also from this operator

Same operator, same x402 payment (USDC on Base), no account:

- [https://keywords.duoleads.com](https://keywords.duoleads.com/llms.txt): keyword research: Google search volume, CPC, difficulty, keyword ideas, Google Trends, $0.03-$0.045 a call
- [https://derivs.duoleads.com](https://derivs.duoleads.com/llms.txt): crypto derivatives: perp funding rates, open interest, basis, liquidations, order books, $0.003-$0.005 a call