KRS Validation in Python

1. What is a KRS number?

KRS (Krajowy Rejestr Sadowy — National Court Register) is a centralised public registry maintained by the Ministry of Justice of Poland. Every company, association, foundation, and certain other legal entities registered in Poland receives a unique KRS number. It serves as the primary identifier in:

• B2B contracts and invoicing between Polish companies
• Public procurement and tender processes
• Due diligence and KYC/AML checks
• Cross-referencing with NIP (tax) and REGON (statistical) registries
• Court filings and legal proceedings

The KRS database is split into two main registries:

2. KRS structure

A KRS number is a simple 10-digit zero-padded sequential number. Unlike NIP or REGON, KRS does not contain a check digit — there is no built-in checksum algorithm to verify structural correctness.

3. Why KRS validation matters

4. The right solution: one API call

The IsValid KRS API handles format validation and government registry lookup 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: KRS Validation API docs →

5. Python code example

Using the isvalid-sdk Python SDK or the requests library. Install with pip install isvalid-sdk or pip install requests.

# krs_validator.py
import os
from isvalid_sdk import IsValidConfig, create_client

iv = create_client(IsValidConfig(api_key=os.environ["ISVALID_API_KEY"]))

# ── Basic validation ────────────────────────────────────────────────────────
result = iv.pl.krs("0000896246")

if not result["valid"]:
    print("Invalid KRS number")
else:
    print(f"KRS: {result['number']}")  # "0000896246"

# ── With government registry lookup ─────────────────────────────────────────
detailed = iv.pl.krs("0000896246", lookup=True)

if detailed["valid"] and detailed.get("krs", {}).get("found"):
    print(f"Name     : {detailed['krs']['name']}")
    print(f"Registry : {detailed['krs']['registry']}")    # "P" or "S"
    print(f"NIP      : {detailed['krs']['nip']}")
    print(f"REGON    : {detailed['krs']['regon']}")
    print(f"City     : {detailed['krs']['address']['city']}")
    print(f"OPP      : {detailed['krs']['hasOppStatus']}")

6. cURL examples

Basic format validation:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/pl/krs?value=0000896246"

With government registry lookup:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/pl/krs?value=0000896246&lookup=true"

7. Understanding the response

Valid KRS (basic)

{
  "valid": true,
  "number": "0000896246"
}

Valid KRS (with lookup)

{
  "valid": true,
  "number": "0000896246",
  "krs": {
    "checked": true,
    "found": true,
    "krs": "0000896246",
    "registry": "P",
    "name": "CREACT.DEV SPÓŁKA Z OGRANICZONĄ ODPOWIEDZIALNOŚCIĄ",
    "legalForm": "SPÓŁKA Z OGRANICZONĄ ODPOWIEDZIALNOŚCIĄ",
    "nip": "5252859428",
    "regon": "388770013",
    "hasOppStatus": false,
    "registeredAt": "2021-04-21",
    "dataAsOf": "2026-01-15",
    "lastEntryAt": "2026-01-14",
    "address": {
      "city": "WARSZAWA",
      "voivodeship": "MAZOWIECKIE",
      "street": "UL. ŚWIĘTOKRZYSKA",
      "houseNumber": "30",
      "flatNumber": "63",
      "postalCode": "00-116",
      "country": "POLSKA",
      "website": "HTTPS://CREACT.DEV/"
    }
  }
}

Invalid KRS

{ "valid": false }

8. Edge cases to handle

# WRONG — loses leading zeros
krs = int("0000028860")  # 28860

# CORRECT — preserve as string
krs = "0000028860"

result = iv.pl.krs("0000896246", lookup=True)

if result["valid"] and result.get("krs", {}).get("found"):
    if result["krs"]["registry"] == "P":
        print("Commercial entity — standard B2B flow")
    elif result["krs"]["registry"] == "S":
        print("Association/foundation — verify OPP status")

result = iv.pl.krs("0000896246", lookup=True)

if result["valid"] and result.get("krs", {}).get("found"):
    if result["krs"]["hasOppStatus"]:
        print("This entity can receive 1.5% tax donations")

result = iv.pl.krs("0000896246", lookup=True)

if result["valid"] and result.get("krs"):
    if not result["krs"]["found"]:
        print("KRS number not found — entity may be dissolved")
    else:
        print(f"Last entry: {result['krs']['lastEntryAt']}")
        print(f"Data as of: {result['krs']['dataAsOf']}")

result = iv.pl.krs("0000896246", lookup=True)

if result["valid"] and result.get("krs", {}).get("found"):
    expected_nip = "5252859428"
    expected_regon = "388770013"

    if result["krs"]["nip"] != expected_nip:
        print("NIP mismatch!")
    if result["krs"]["regon"] != expected_regon:
        print("REGON mismatch!")