WKN Validation in Python

1. What is a WKN?

A WKN (Wertpapierkennnummer — also written WPKN or WPK) is the 6-character alphanumeric identifier used to identify securities in Germany. Issued since 1968 by WM Datenservice (formerly Wertpapier-Mitteilungen) in Frankfurt, WKNs appear in German brokerage confirmations, bank statements, portfolio reports, and financial data feeds.

While ISIN has become the standard for cross-border and regulatory reporting (MiFID II, EMIR), WKNs remain pervasive in the German retail and private banking segment. Many German brokers, neo-banks, and wealth management platforms expose WKNs alongside ISINs — and some legacy systems expose WKNs only.

Unlike ISIN, CUSIP, or SEDOL, the WKN has no check digit. It is an opaque sequence — there is no algorithm to verify structural correctness. Confirming a WKN requires a database lookup.

2. WKN anatomy

A WKN is exactly 6 characters long, using digits and uppercase letters:

Some well-known examples:

3. WKN inside a German ISIN

German ISINs embed the WKN in a predictable way. The NSIN (National Securities Identifying Number) portion of a DE ISIN is the WKN zero-padded on the left to 9 characters:

# Extracting WKN from a German ISIN
isin = "DE0005140008"

country = isin[:2]   # "DE"
nsin    = isin[2:11] # "000514000"
check   = isin[11]   # "8"

# The WKN is the NSIN with leading zeros stripped
wkn = nsin.lstrip("0")  # "514000"

print(wkn)  # → 514000

4. Why format checks are not enough

5. The right solution: one API call

The IsValid WKN API combines format validation and live OpenFIGI enrichment in a single GET /v0/wkn request.

Get your free API key at isvalid.dev.

Full parameter reference and response schema: WKN Validation API docs →

6. Python code example

Using the isvalid-sdk package or the requests library directly.

# wkn_validator.py
import os
from isvalid_sdk import IsValid

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

# ── Example usage ─────────────────────────────────────────────────────────────

result = iv.wkn("514000")  # Deutsche Bank AG

if not result["valid"]:
    print("Invalid WKN: must be 6 alphanumeric characters")
else:
    print(f"WKN         : {result['wkn']}")
    if result.get("found"):
        print(f"Name        : {result.get('name')}")
        print(f"ISIN        : {result.get('isin')}")
        print(f"Ticker      : {result.get('ticker')}")
        print(f"Exchange    : {result.get('exchCode')}")
        print(f"FIGI        : {result.get('figi')}")
        print(f"Sector      : {result.get('marketSector')}")

Expected output for 514000:

WKN         : 514000
Name        : Deutsche Bank AG
ISIN        : DE0005140008
Ticker      : DBK
Exchange    : GY
FIGI        : BBG000BC5588
Sector      : Equity

# router.py (FastAPI)
from fastapi import APIRouter, HTTPException
import requests, os

router = APIRouter()
API_KEY = os.environ["ISVALID_API_KEY"]


@router.get("/securities/validate-wkn")
def validate_wkn_endpoint(wkn: str):
    if not wkn:
        raise HTTPException(status_code=400, detail="Missing wkn parameter")

    try:
        resp = requests.get(
            "https://api.isvalid.dev/v0/wkn",
            params={"value": wkn},
            headers={"Authorization": f"Bearer {API_KEY}"},
            timeout=10,
        )
        resp.raise_for_status()
        result = resp.json()
    except requests.RequestException:
        raise HTTPException(status_code=502, detail="WKN validation service unavailable")

    if not result["valid"]:
        raise HTTPException(status_code=400, detail=f"Invalid WKN: {wkn}")

    return {
        "wkn": result["wkn"],
        "found": result.get("found"),
        "isin": result.get("isin"),
        "name": result.get("name"),
        "ticker": result.get("ticker"),
        "exchCode": result.get("exchCode"),
        "figi": result.get("figi"),
    }

7. cURL example

Deutsche Bank AG:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/wkn?value=514000"

SAP SE:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/wkn?value=716460"

Invalid format:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/wkn?value=5140"

8. Understanding the response

Response for a valid WKN found in OpenFIGI:

{
  "valid": true,
  "wkn": "514000",
  "found": true,
  "dataSource": "openfigi",
  "isin": "DE0005140008",
  "name": "Deutsche Bank AG",
  "ticker": "DBK",
  "exchCode": "GY",
  "securityType": "Common Stock",
  "marketSector": "Equity",
  "figi": "BBG000BC5588",
  "compositeFIGI": "BBG000BC5588"
}

Response for an invalid WKN:

{
  "valid": false
}

9. Edge cases to handle

10. Summary

• ISIN validation — ISINs embed WKNs for DE-prefixed codes
• SEDOL validation — the UK equivalent
• CUSIP validation — the North American equivalent
• WKN Validation in Node.js

Python integration notes

Use Pydantic V2's @field_validator or the Annotated + AfterValidator pattern to embed WKN validation in your data models. The validator calls the IsValid API and raises a ValueError if valid is False. Because there is no check digit to compute locally, the API call is the only meaningful validation step — format-only regex checks provide little protection against real-world errors.

• Store ISVALID_API_KEY in a .env file and load with python-dotenv
• Cache results in Redis with a 24h TTL — WKN-to-instrument mappings rarely change
• Apply .strip().upper() before validation to normalise input from different source systems
• Use NewType('Wkn', str) to distinguish validated WKNs from raw strings in type annotations
• Store the isin field from the response — it enables downstream cross-referencing without additional API calls