Korean & Japanese Business Number Validator
Check a Korean business registration number (사업자등록번호), a Japanese corporate number (法人番号) or a Japanese qualified-invoice registration number (the T-number) against the checksum it is supposed to carry. All three encode a check digit, so a typo, a transposition or an invented number can be caught with arithmetic alone — no government API, no registration key, no rate limit, and nothing leaving your browser. Paste one number, or a whole supplier list.
El dígito de control se calcula en tu navegador. A diferencia de los servicios gubernamentales de verificación por los que suelen pasar estos números - la API 진위확인 de data.go.kr en Corea y la Web-API 法人番号 en Japón, ambas con clave registrada requerida - no se envía nada a ningún sitio, no hay límite de peticiones, y una lista de miles se valida al instante.
Nada que comprobar todavía
Los tres formatos
Diez dígitos. Los primeros tres son la oficina tributaria emisora, los dos siguientes indican el tipo de entidad (81 y 86-88 son sedes con fines de lucro, 82 organizaciones sin fines de lucro, 90-99 autónomos exentos de impuestos), los siguientes cuatro son un número de serie, y el último es el dígito de control.
Trece dígitos, y de forma inusual el dígito de control va primero. Los doce restantes son el 会社法人等番号 de la empresa, del registro mercantil. Toda empresa registrada tiene uno y el registro completo es público.
Introducido con el sistema インボイス制度 de 2023. Es una T seguida de los mismos 13 dígitos, y un comprador japonés lo necesita en tu factura para recuperar el impuesto al consumo - por eso vale la pena comprobarlo antes de declarar.
What a check digit proves, and what it does not
A check digit is a digit computed from the rest of the number by a published formula. If the number you have does not carry the digit the formula demands, something is wrong with the digits — almost always a mistyped or swapped pair. That makes this a very good filter for data-entry errors before you file a tax return, issue an invoice or import a supplier list.
What it cannot do is tell you whether the business is real. A checksum-valid number may belong to nobody, or to a company that dissolved a decade ago, or to a completely different firm than the one on your invoice. Only the registry can answer that: Korea's 국세청 (National Tax Service) for a BRN, and Japan's 法人番号公表サイト for a corporate number — the latter is fully public and searchable, and this tool links straight into it for any number that passes.
The two algorithms
🇰🇷 사업자등록번호
Multiply the first nine digits by the weights 1, 3, 7, 1, 3, 7, 1, 3, 5 and add them up. Then add the tens digit of the ninth digit's own product — the carry term everyone forgets, and the reason so many home-made validators reject valid numbers. The check digit is 10 minus the total mod 10, mod 10.
124810099 → 118 + 4 = 122 → 10 − 2 = 8 → 124-81-00998 ✓
🇯🇵 法人番号
Number the twelve-digit base from its rightmost digit. Add the digits in odd positions, add twice the digits in even positions, and the check digit is 9 minus that total mod 9. Unusually, the check digit is written first, not last.
700110005901 → 11 + 26 = 37 → 9 − 1 = 8 → 8700110005901 ✓
Both are the published official rules — Korea's from the National Tax Service's long-mirrored reference implementation, Japan's from the National Tax Agency's own check-digit note, whose worked example is one of the samples above.
Preguntas frecuentes
How do I check whether a Korean business registration number is valid?
Paste it in - with or without the 123-45-67890 hyphens, spaces or full-width digits, all of which are handled. The tool applies the National Tax Service's published check-digit formula to the first nine digits and compares the result with the tenth. If they match the number is internally consistent; if they do not, you are told both what the number carries and what the algorithm requires, which usually points at a single mistyped digit. It also decodes the structure for you: the first three digits are the issuing tax office, and the middle two are the entity type - 81 and 86 to 88 mean a for-profit corporation's head office, 82 a non-profit, 84 a foreign company's Korean branch, and 90 to 99 a tax-exempt sole trader.
What is a Japanese corporate number (法人番号), and why does the check digit come first?
It is a 13-digit identifier the National Tax Agency assigns to every registered company, government body and certain other organisations in Japan, introduced in 2015. The last twelve digits are the entity's existing 会社法人等番号 from the commercial register, and the check digit is prepended rather than appended precisely because those twelve digits already existed and could not be renumbered. The entire registry is public and searchable at the NTA's 法人番号公表サイト, which is unusual - a valid number can be confirmed against a real company name and address for free, with no key.
What is a Japanese invoice T-number, and why does it matter?
Japan's qualified invoice system (インボイス制度) started on 1 October 2023. Under it, a business can only reclaim the consumption tax on a purchase if the invoice carries the seller's registration number - a T followed by 13 digits. For a company that is simply its corporate number with a T in front; a sole trader gets a separately assigned 13-digit number that carries the same check digit. If you sell to Japanese businesses, your T-number goes on your invoices; if you buy from Japanese suppliers, a wrong or missing one is a real tax problem, which is why checking the digits before filing is worth the thirty seconds.
Can I check a whole list at once?
Yes. Switch to the bulk tab and paste one number per line - the three formats can be mixed, and each line is detected on its own. You get a count of valid, invalid and unrecognised, a row-by-row table showing the check digit each number carries against the one it should, and a CSV export with all of it. Because the maths runs locally, a list of several thousand numbers finishes instantly; there is no per-request quota to work around.
Why not just use the government API?
Because both of them need a registration you probably do not want for a one-off check. Korea's 사업자등록정보 진위확인 service on data.go.kr requires an approved service key, and Japan's 法人番号 Web-API requires a separate application. Both are also rate-limited and both mean sending your supplier list to a third party. The check digit is a published formula, so for catching typos - which is the overwhelming majority of what goes wrong - the arithmetic is enough, and it works offline. Use the registries for the thing only they can do: confirming a valid-looking number belongs to the company you think it does.
The number I have is 12 digits, not 13. What is it?
Almost certainly a 会社法人等番号 - the company registration number from Japan's commercial register, which predates the corporate-number system and is still printed on registry extracts and company seals. It is the base of the corporate number without its leading check digit. Paste it in and the tool computes the check digit for you and shows the full 13-digit corporate number it produces, so you can go straight to looking it up.
Is my data uploaded anywhere?
No. The check digit is computed in JavaScript on your own device, and no number you paste - single or bulk - is ever transmitted. Once the page has loaded, the tool works with your connection off. That is deliberate: a supplier list is commercially sensitive, and there is no good reason to send one to a server to do arithmetic that fits in a few lines of code.