When to use it
A new vendor sends over their Korean Business Registration Number (BRN) and you want to confirm in ten seconds that the format is right. Or you have a 200-row spreadsheet of BRNs and need to spot the typos, format errors, and duplicates in one pass.
What this checks
Only the checksum. Whether the last digit of the 10-digit BRN matches the value derived from the first nine. Whether the business actually exists, whether it's open or closed, whether it's standard / simplified / exempt for VAT — this tool cannot tell you that. For status, use Hometax → '사업자상태 조회'.
Algorithm
weights = [1, 3, 7, 1, 3, 7, 1, 3, 5]
sum = Σ digits[i] * weights[i] (i = 0..8)
sum += floor(digits[8] * 5 / 10) // 9th-digit correction
checkDigit = (10 - sum mod 10) mod 10
valid = checkDigit == digits[9]
The National Tax Service's standard. Zero external libraries.
Type inference (4·5 digits)
| 4·5 digits | Inferred type | |---|---| | 01–79 | Sole proprietor | | 80 | MLM / trust operator | | 81–84 | Corporate HQ (for-profit) | | 85 | Unit-tax taxpayer | | 86–87 | Corporate branch | | 89 | Non-profit HQ | | 90–99 | Non-profit branch |
Edge cases exist (the table evolves and partial overlaps are possible), so the result is labeled "inferred."
Bulk mode
One per line, or separated by comma, semicolon, or whitespace. The results table copies to CSV (paste directly into Excel). Keep it under ~1,000 rows for UI responsiveness.
Privacy
Vendor lists, bulk BRNs, and validation results are not transmitted — the algorithm is just multiplication and modulo. Zero external calls, including no Hometax API.
Not the right tool when
- Confirming a business is actually registered — checksum is form only. For real existence, active/closed status, and tax type, use Hometax or call ARS 1588-0560.
- Verifying invoice eligibility — separate concern. Ask the vendor or check Hometax directly.
- Resident-registration number validation — intentionally not offered. Personal-information territory, and a checksum doesn't equal identity verification.
- Foreigner-registration or corporate-registration numbers — those use different algorithms and are not supported here.
BRNs stay on the page
Vendor lists, bulk BRNs, and validation results are not transmitted. The check is just weighted multiplication and modulo arithmetic — zero external libraries. Hometax's business-status API is never called.