Provided as is, without warranty — see DISCLAIMER.md.
Zero-dependency TypeScript validators for Czech identifiers: IČO, DIČ, rodné číslo, domestic bank account numbers (with the ČNB bank-code list and conversion to/from IBAN), IBAN for all registry countries, and PSČ. Every rule is taken from a cited primary source, and every result is typed.
🇨🇿 Validace a normalizace českých identifikátorů: IČO, DIČ, rodné číslo, číslo účtu (včetně seznamu kódů bank ČNB a převodu na IBAN), IBAN a PSČ. Pravidla podle vyhlášky ČNB 169/2011 Sb., zákona 133/2000 Sb. a dalších uvedených zdrojů.
- Correct edge cases: IČO remainder 0/1/10, the rodné číslo remainder-10 exception, the +20/+70 month series since 2004, 9-digit numbers before 1954, leap days, bank accounts with insignificant leading zeros.
- Typed results, not just booleans: normalized and formatted values, birth date and sex from a rodné číslo, bank name and BIC for an account, the kind of a DIČ and whether its checksum could actually be verified.
- Typed errors with stable codes (
InvalidChecksum,InvalidDate, …) that never echo the input back, so they are safe to log. - Bundled reference data with provenance: ČNB bank codes and the SWIFT IBAN Registry country table, committed as source files with dates and URLs.
- Tiny: no runtime dependencies, ESM + CJS, tree-shakeable.
Not published to npm yet. Install a tagged release from GitHub (npm builds the package during installation):
npm install github:gildor853/cz-validators#v1.0.0Requires Node.js 18+, or any modern browser / edge runtime (the code uses no Node.js APIs).
The published package has no runtime dependencies and is verified on Node.js 18 and 20 by a runtime smoke test in CI. Development (tests) needs Node.js 22.12+, as required by vitest 5.
import {
parseIco,
parseDic,
parseRodneCislo,
parseBankAccount,
ibanToBankAccount,
parseIban,
parsePsc,
tryParseIco,
} from "cz-validators";
parseIco("481 364 50");
// { value: "48136450" }
parseDic("cz48136450");
// { value: "CZ48136450", digits: "48136450", kind: "legal-entity", checksumVerified: true }
parseRodneCislo("905715/1235"); // synthetic example
// { value: "9057151235", formatted: "905715/1235", length: 10,
// birthDate: "1990-07-15", sex: "female", supplementarySeries: false, checksumException: false }
parseBankAccount("19-2000145399/0800");
// { prefix: "19", number: "2000145399", bankCode: "0800",
// formatted: "19-2000145399/0800", bankName: "Česká spořitelna, a.s.",
// bic: "GIBACZPX", iban: "CZ6508000000192000145399" }
ibanToBankAccount("CZ69 0710 1781 2400 0000 4159").formatted;
// "178124-4159/0710"
parseIban("gb29 nwbk 6016 1331 9268 19");
// { value: "GB29NWBK60161331926819", formatted: "GB29 NWBK 6016 1331 9268 19",
// country: "GB", checkDigits: "29", bban: "NWBK60161331926819" }
parsePsc("11000").formatted; // "110 00"
const r = tryParseIco("48136451");
if (!r.ok) console.log(r.error.code); // "InvalidChecksum"Every identifier has the same three functions:
| Function | Returns | On invalid input |
|---|---|---|
parseX(input, options?) |
frozen value object | throws CzValidatorError |
tryParseX(input, options?) |
{ ok: true, value } | { ok: false, error } |
never throws |
isValidX(input, options?) |
boolean |
– |
Whitespace (including no-break spaces) is ignored everywhere.
Returns { value } (8 digits). Seven-digit legacy numbers must be written
with their leading zero, as ARES does. icoCheckDigit(firstSeven) returns
the check digit.
Rule: weights 8, 7, 6, 5, 4, 3, 2 on the first seven digits,
r = sum mod 11, check digit (11 − r) mod 10, i.e. r = 0 → 1,
r = 1 → 0, r = 10 → 1, otherwise 11 − r. Example: ČNB, IČO 48136450,
sum 155, r = 1, check digit 0.
Returns { value: "CZ…", digits, kind, checksumVerified }. The CZ prefix
is optional in the input ({ requirePrefix: true } to require it) and
always present in value.
| Numeric part | kind |
What is validated |
|---|---|---|
| 8 digits | legal-entity |
IČO check digit (the DIČ equals the IČO) |
| 9 digits starting with 6 | special |
format only (checksumVerified: false): VAT groups CZ699nnnnnk and numbers assigned by the tax office ("VČP"); the check-digit algorithm is not published |
| other 9 or 10 digits | individual |
full rodné číslo validation (the DIČ equals the RČ) |
Limits: since 2021 an individual (and also a legal entity) may have a DIČ based on a VČP instead of the RČ/IČO. The format of a VČP is not published; VČP-based numbers that do not start with 6 and do not happen to satisfy the IČO/RČ rules are rejected. Validation never proves VAT registration; use the ADIS register or VIES for that.
Returns { value, formatted, length, birthDate, sex, supplementarySeries, checksumException }.
Accepts YYMMDDXXXX, YYMMDD/XXXX and the 9-digit forms.
- 10 digits: the whole number must be divisible by 11. Historical exception:
if the first nine digits leave remainder 10, the check digit 0 is accepted
(
checksumException: true), only for birth years up to 1985, when issuing such numbers stopped. - 9 digits: only for births before 1954, no check digit, ending 001–999.
- Month: 1–12 men, +50 women; since 2004 also +20 men / +70 women
(
supplementarySeries: true). - The birth date must exist (leap years included).
- Century: 9-digit → 1900–1953. 10-digit → 1954–1999 for
YY ≥ 54; forYY ≤ 53it is 20YY unless that date would be afteroptions.referenceDate(default: now), then 19YY (10-digit numbers were assigned later to some people born before 1954).
Privacy. A rodné číslo is personal data and reveals birth date and sex. Do not log it, do not put it in URLs or analytics, and store it only where you have a legal basis to do so (GDPR; § 13c of zákon 133/2000 Sb. limits who may use it). This library never includes the input in error messages. All examples and tests in this repository use synthetic numbers.
Parses [prefix-]number/bankCode and returns
{ prefix, number, bankCode, formatted, bankName, bic, iban }.
- prefix: optional, up to 6 digits; base number: 2–10 digits with at least two
non-zero digits; leading zeros are insignificant and removed in
formatted; - both parts must pass the weighted mod-11 check (weights 6, 3, 7, 9, 10, 5,
8, 4, 2, 1 on the digits right-aligned to 10 places; the sum must be
divisible by 11).
isValidAccountPart(digits)exposes the check; - bank code: exactly 4 digits. Unknown codes are accepted (with
bankName: undefined) unless{ requireKnownBankCode: true }.
Conversions:
bankAccountToIban(accountOrParts)→{ electronic, formatted }; accepts a string or{ prefix?, number, bankCode }.ibanToBankAccount(iban)/tryIbanToBankAccount(iban)→ the same object asparseBankAccount; non-CZ IBANs fail withUnsupportedCountry.
A CZ IBAN is CZ + 2 check digits + bank code (4) + prefix (6) + number
(10), 24 characters.
getBank("0800") → { code, name, bic, certis } or undefined.
BANK_CODES_META records the source URL, retrieval date (2026-10-09) and
the file's last-modified date at ČNB (2026-09-25). The list changes from time
to time; the original CSV is committed in data/ and
npm run gen:data regenerates the TypeScript table.
Returns { value, formatted, country, checkDigits, bban }, where value is
the electronic format and formatted the print format (groups of four).
Checks: characters, per-country length and BBAN structure from the SWIFT
IBAN Registry, and ISO 7064 MOD 97-10. Countries outside the registry fail
with UnsupportedCountry unless { allowUnknownCountry: true }.
Helpers: ibanCheckDigits(country, bban), ibanMod97(iban),
formatIbanGroups(electronic), getIbanCountryFormat(country),
listIbanCountries() (89 countries).
Returns { value: "11000", formatted: "110 00" }. Five digits, first digit
1–7 (0, 8 and 9 belong to the Slovak series of the former common system).
This is a format check only, not a claim that the code exists.
All failures are CzValidatorError with:
code:InvalidFormat|InvalidLength|InvalidChecksum|InvalidDate|InvalidComponent|UnknownBankCode|UnsupportedCountrykind:ico|dic|rodne-cislo|bank-account|iban|psc
Non-string input fails with InvalidFormat. Messages never contain the input.
import { tryParseBankAccount } from "cz-validators";
function accountError(userInput: string): string | null {
const r = tryParseBankAccount(userInput);
if (r.ok) return null;
switch (r.error.code) {
case "InvalidChecksum": return "Číslo účtu nemá platnou kontrolní číslici.";
case "InvalidFormat": return "Zadejte účet ve tvaru předčíslí-číslo/kód banky.";
default: return "Neplatné číslo účtu.";
}
}
accountError("19-2000145399/0800"); // null
accountError("19-2000145398/0800"); // "Číslo účtu nemá platnou kontrolní číslici."| Topic | Source |
|---|---|
| Bank account format and check algorithm | Vyhláška ČNB č. 169/2011 Sb., § 5–6 and annex (PDF at cnb.cz) |
| CZ IBAN structure | Vyhláška č. 169/2011 Sb., § 4; ČNB, IBAN – mezinárodní formát čísla účtu (examples used in tests) |
| Bank codes | ČNB, Kódy bank / platebního styku, CSV retrieved 2026-10-09 |
| IBAN check digits and country formats | ISO 13616 / ISO 7064; SWIFT IBAN Registry release 101 (see data/iban-registry.txt for how it was transcribed) |
| Rodné číslo | Zákon č. 133/2000 Sb., o evidenci obyvatel, § 13; MV ČR, Rodné číslo; remainder-10 exception: DASTA/NZIS, Struktura rodného čísla |
| DIČ | Zákon č. 280/2009 Sb., daňový řád, § 130; Finanční správa, nápověda registru plátců DPH and Informace ke skupinové registraci (format CZ699nnnnnk) |
| IČO check digit | Weighted mod-11 as used by ARES / ČSÚ; cross-checked against published IČOs (e.g. ČNB 48136450) |
| PSČ | Česká pošta numbering; leading-digit regions per cs.wikipedia: Poštovní směrovací číslo |
- All checks are offline and structural. A valid result does not mean the company, person, account, IBAN or postal code exists or is active.
- DIČ numbers based on a VČP are only partly supported (see above).
- The bundled bank-code list and IBAN registry are snapshots; new bank codes
or IBAN countries need a library update (or
allowUnknownCountry). - The rodné číslo rules cover numbers assigned under Czech (and former Czechoslovak) rules; possible future changes to the format are not covered.
Use at your own risk. This software is provided as is, without warranty of any kind. It is not legal or tax advice. Verify identifiers against official registers. See the full legal text in DISCLAIMER.md.
This repository is maintained by a single author and does not accept external contributions; issues and pull requests are limited to collaborators.
Security problems can be reported privately, see SECURITY.md.
MIT © 2026 Gildor