Does this tool send my data anywhere?

No. Every calculation is pure arithmetic running in your browser. There is no network request, no logging and no API key involved.

Does a valid check digit mean the company exists?

No, and this is the important limitation. A check digit only proves the number is internally consistent - it says nothing about whether that number was ever issued to a real company. To know that, you have to look it up in the registry.

Can you validate an EU VAT number offline?

Only its structure, plus the national check digit where one exists (Spain, Poland, and the SIREN inside a French VAT number). Whether the number is registered and active can only be confirmed against VIES, the EU VAT information exchange system, which requires a server-side call.

European company identifier validator — free, offline

Check the check digit on a Spanish NIF or CIF, a French SIREN or SIRET, a Polish NIP or REGON, a Norwegian organisation number, a UK company number, an Irish CRO number, or any EU VAT number. Free, no signup, and no data leaves your browser — every calculation runs locally.

Which identifiers actually have a check digit

This distinction matters more than most tools admit. Spain (NIF/CIF/NIE), France (SIREN/SIRET), Poland (NIP/REGON) and Norway (organisasjonsnummer) all carry a real check digit, so a typo can be caught offline before it costs an API call. UK company numbers and Irish CRO numbers do not. For those, a validator can only confirm the shape is right — it cannot tell you the company exists. Any tool that reports a UK company number as "valid" is overstating what it checked.

EU VAT numbers

Structure is checked per country, and where the national number is itself checksummed — Spain, Poland, and the SIREN inside a French VAT number — that check runs too. Whether a VAT number is actually registered and active can only be answered by VIES, which requires a server-side call.

Why it is free

It is pure arithmetic. There is no lookup, no API key and no cost to run it, so there is no reason to put it behind a signup. If you then need to know whether the company exists, who its directors are, or whether it is under insolvency proceedings, that is what the Prometiam API does across Spain, France, the UK, Ireland, Poland and Norway.

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Which identifiers actually have a check digit

Identifier	Check digit?	Algorithm
Spain — NIF / CIF / NIE	Yes	Letter from mod 23 (personal), or weighted digit sum (company)
France — SIREN	Yes	Luhn over 9 digits
France — SIRET	Yes	Luhn over 14 digits (La Poste is a documented exception)
Poland — NIP	Yes	Weighted sum mod 11
Poland — REGON	Yes	Weighted sum mod 11 (9 and 14-digit forms)
Norway — organisasjonsnummer	Yes	Weighted sum mod 11
UK — company number	No	Format only — 8 digits, or 2 letters + 6 digits
Ireland — CRO number	No	Format only — a plain sequential integer
EU VAT	Varies	Per-country structure, plus the national check digit where one exists

Frequently asked questions

Which European company identifiers have a check digit?: Spain (NIF, CIF and NIE), France (SIREN and SIRET, both Luhn), Poland (NIP and REGON) and Norway (organisasjonsnummer, modulo 11) all carry a real check digit, so a typo can be caught offline. UK company numbers and Irish CRO numbers carry no check digit at all - for those, only the format can be checked.
Does this tool send my data anywhere?: No. Every calculation is pure arithmetic running in your browser. There is no network request, no logging and no API key involved.
Does a valid check digit mean the company exists?: No, and this is the important limitation. A check digit only proves the number is internally consistent - it says nothing about whether that number was ever issued to a real company. To know that, you have to look it up in the registry.
Can you validate an EU VAT number offline?: Only its structure, plus the national check digit where one exists (Spain, Poland, and the SIREN inside a French VAT number). Whether the number is registered and active can only be confirmed against VIES, the EU VAT information exchange system, which requires a server-side call.