CEIDG Validation in Node.js

1. What is CEIDG?

CEIDG (Centralna Ewidencja i Informacja o Działalności Gospodarczej — Central Registration and Information on Business Activity) is the official Polish government registry for:

• Sole proprietors (JDG — jednoosobowa działalność gospodarcza)
• Civil partnerships (spółki cywilne) — each partner registers separately

CEIDG does not cover companies incorporated under commercial law (sp. z o.o., S.A., sp. k., etc.) — those are registered in the KRS (National Court Register). If you receive a NIP and do not know the entity type, start with CEIDG; if not found, fall back to KRS.

CEIDG is maintained by the Ministry of Economic Development and is publicly accessible. It stores:

• Owner's first and last name
• Business name (if different from the owner's name)
• Registration status (active / suspended / deleted)
• Registered business address
• PKD activity codes (Polish Classification of Activities, based on NACE Rev. 2)
• REGON statistical number and NIP tax number
• Business commencement date

2. NIP — the key identifier

CEIDG entries are identified by NIP (Numer Identyfikacji Podatkowej — Tax Identification Number), the Polish equivalent of a VAT/tax ID. A NIP is:

• Exactly 10 digits, no letters
• Written with hyphens as NNN-NNN-NN-NN (e.g. 526-104-08-28)
• Protected by a MOD-11 weighted checksum on the last digit

3. The NIP MOD-11 checksum algorithm

The NIP checksum uses a weighted MOD-11 algorithm. The first 9 digits are each multiplied by a fixed weight, the products are summed, and the result modulo 11 must equal the 10th (check) digit. If the remainder is 10, the number is always invalid.

function nipValid(nip) {
  const digits = nip.replace(/[\-\s]/g, '').split('').map(Number);
  if (digits.length !== 10) return false;
  const weights = [6, 5, 7, 2, 3, 4, 5, 6, 7];
  const sum = weights.reduce((acc, w, i) => acc + digits[i] * w, 0);
  const check = sum % 11;
  return check !== 10 && check === digits[9];
}

4. Worked example — step by step

Let's verify NIP 526-104-08-28 (digits: 5261040828):

5. Why format checks alone are not enough

6. The right solution: one API call

The IsValid CEIDG API handles the full validation and lookup stack in a single GET request:

Get your free API key at isvalid.dev. The free tier includes 100 calls per day with no credit card required.

Full parameter reference and response schema: CEIDG API docs →

7. Node.js code example

Using the @isvalid-dev/sdk package or the built-in fetch API (Node.js 18+):

// ceidg-validator.mjs
import { createClient } from '@isvalid-dev/sdk';

const iv = createClient({ apiKey: process.env.ISVALID_API_KEY });

// ── NIP checksum validation only ────────────────────────────────────────────
const result = await iv.pl.ceidg('9876543210');

if (!result.valid) {
  console.log('Invalid NIP');
} else {
  console.log('NIP:', result.nip); // "987-654-32-10"
}

// ── With CEIDG registry lookup ───────────────────────────────────────────────
const detailed = await iv.pl.ceidg('9876543210', { lookup: true });

if (detailed.valid && detailed.ceidg?.found) {
  const c = detailed.ceidg;
  console.log('Owner    :', c.firstName, c.lastName);
  console.log('Business :', c.businessName);
  console.log('Status   :', c.status);      // "active" | "suspended" | "deleted"
  console.log('City     :', c.city);
  console.log('PKD      :', c.primaryPkd);  // e.g. "70.22.Z"
  console.log('All PKD  :', c.pkd);         // ["70.22.Z", "74.90.Z", ...]
}

8. cURL examples

NIP checksum validation only:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/pl/ceidg?value=9876543210"

With CEIDG registry lookup:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/pl/ceidg?value=9876543210&lookup=true"

Hyphens are accepted and stripped automatically:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/pl/ceidg?value=987-654-32-10"

9. Understanding the response

Valid NIP (checksum only)

{
  "valid": true,
  "nip": "987-654-32-10"
}

Valid NIP with CEIDG lookup

{
  "valid": true,
  "nip": "987-654-32-10",
  "ceidg": {
    "checked": true,
    "found": true,
    "status": "active",
    "firstName": "JAN",
    "lastName": "KOWALSKI",
    "businessName": "JK CONSULTING JAN KOWALSKI",
    "regon": "146123456",
    "city": "Warszawa",
    "postalCode": "00-001",
    "street": "Marszałkowska",
    "houseNumber": "1",
    "flatNumber": null,
    "startDate": "2015-03-01",
    "pkd": ["70.22.Z", "74.90.Z", "63.11.Z"],
    "primaryPkd": "70.22.Z"
  }
}

NIP not found in CEIDG

{
  "valid": true,
  "nip": "526-104-08-28",
  "ceidg": {
    "checked": true,
    "found": false
  }
}

Invalid NIP

{ "valid": false }

10. Edge cases to handle

const result = await validateCeidg(nip, { lookup: true });

if (result.valid && result.ceidg?.found) {
  if (result.ceidg.status !== 'active') {
    // Business is suspended or deleted — do not onboard
    return {
      status: 'rejected',
      reason: `CEIDG status: ${result.ceidg.status}`,
    };
  }
  // Proceed with onboarding
}

const ceidg = await validateCeidg(nip, { lookup: true });

if (ceidg.valid && ceidg.ceidg?.checked && !ceidg.ceidg.found) {
  // Not a sole proprietor — try VAT/VIES for companies
  const vat = await iv.vat(`PL${nip}`, { checkVies: true });
  if (vat.valid && vat.vies?.valid) {
    console.log('KRS company confirmed via VIES:', vat.vies.name);
  }
}

const result = await validateCeidg(nip, { lookup: true });

if (result.valid && result.ceidg && !result.ceidg.checked) {
  // CEIDG API temporarily unavailable
  await scheduleRecheck(nip, '1h');
  return { status: 'provisional', reason: 'ceidg_unavailable' };
}

// All of these are accepted and produce the same result:
await validateCeidg('9876543210');
await validateCeidg('987-654-32-10');
await validateCeidg('987 654 32 10');