CEIDG Validation in Python

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.

import re


def nip_valid(nip: str) -> bool:
    digits = [int(c) for c in re.sub(r"[\-\s]", "", nip)]
    if len(digits) != 10:
        return False
    weights = [6, 5, 7, 2, 3, 4, 5, 6, 7]
    total = sum(d * w for d, w in zip(digits, weights))
    check = total % 11
    return check != 10 and 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. Python code example

Using the requests library or the standard urllib.request:

# ceidg_validator.py
import os
import requests

API_KEY = os.environ["ISVALID_API_KEY"]
BASE_URL = "https://api.isvalid.dev"


def validate_ceidg(nip: str, lookup: bool = False) -> dict:
    params = {"value": nip}
    if lookup:
        params["lookup"] = "true"
    response = requests.get(
        f"{BASE_URL}/v0/pl/ceidg",
        params=params,
        headers={"Authorization": f"Bearer {API_KEY}"},
        timeout=10,
    )
    response.raise_for_status()
    return response.json()


# ── NIP checksum validation only ────────────────────────────────────────────
result = validate_ceidg("9876543210")

if not result["valid"]:
    print("Invalid NIP")
else:
    print("NIP:", result["nip"])  # "987-654-32-10"

# ── With CEIDG registry lookup ───────────────────────────────────────────────
detailed = validate_ceidg("9876543210", lookup=True)

if detailed["valid"] and detailed.get("ceidg", {}).get("found"):
    c = detailed["ceidg"]
    print("Owner    :", c["firstName"], c["lastName"])
    print("Business :", c["businessName"])
    print("Status   :", c["status"])       # "active" | "suspended" | "deleted"
    print("City     :", c["city"])
    print("PKD      :", c["primaryPkd"])   # e.g. "70.22.Z"
    print("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

result = validate_ceidg(nip, lookup=True)

ceidg = result.get("ceidg") or {}
if result["valid"] and ceidg.get("found"):
    if ceidg["status"] != "active":
        # Business is suspended or deleted — do not onboard
        raise ValueError(f"CEIDG status: {ceidg['status']}")
    # Proceed with onboarding

ceidg = validate_ceidg(nip, lookup=True)
ceidg_data = ceidg.get("ceidg") or {}

if ceidg["valid"] and ceidg_data.get("checked") and not ceidg_data.get("found"):
    # Not a sole proprietor — try VAT/VIES for companies
    vat = validate_vat(f"PL{nip}", check_vies=True)
    if vat["valid"] and (vat.get("vies") or {}).get("valid"):
        print("KRS company confirmed via VIES:", vat["vies"]["name"])

result = validate_ceidg(nip, lookup=True)
ceidg = result.get("ceidg") or {}

if result["valid"] and ceidg and not ceidg.get("checked"):
    # CEIDG API temporarily unavailable
    schedule_recheck(nip, delay="1h")
    return {"status": "provisional", "reason": "ceidg_unavailable"}

REQUIRED_PKD = {"64", "65", "66"}  # financial services divisions

result = validate_ceidg(nip, lookup=True)
ceidg = result.get("ceidg") or {}

if ceidg.get("found"):
    pkd_divisions = {code[:2] for code in ceidg.get("pkd", [])}
    if not REQUIRED_PKD & pkd_divisions:
        raise ValueError(
            f"Entity does not hold required financial services PKD codes. "
            f"Has: {pkd_divisions}"
        )