France SIRET validator
How the SIRET format works
- Format
- 14-digit French establishment identifier (Luhn check digit)
- Example
- 55210055400013
Things to watch for
- 14 digits: a 9-digit SIREN plus a 5-digit NIC (establishment number) — the full 14-digit string passes a standard Luhn check
- One documented exception: La Poste's own SIREN (356000000) uses a non-Luhn checksum rule, which this validator (like most generic tools) does not special-case
- Format and checksum only — it doesn't confirm the establishment is active; check the official Sirene / annuaire-entreprises directory for that
^[0-9]{14}$A SIRET is the 14-digit number that identifies one specific physical establishment of a French business — a particular shop, factory, or office — rather than the business as a whole. It’s built by taking the company’s 9-digit SIREN and appending a 5-digit NIC, so a retailer with a head office and a dozen store locations has one SIREN but a distinct SIRET for every single site.
Checking all 14 digits together
Unlike the SIREN, whose Luhn check runs over 9 digits, a SIRET’s Luhn calculation runs across the full 14-digit string — the SIREN and the NIC together, not each part separately. That means changing either half changes what the check digit needs to be, which is exactly what lets this validator catch a mistyped digit in either the business identifier or the establishment code.
A documented exception worth knowing
Not every real SIRET follows the standard rule: entities registered under the SIREN 356000000, most notably La Poste, use their own established checksum convention rather than the standard Luhn calculation. It’s a narrow, well-documented carve-out — most SIRETs outside that one SIREN follow the standard rule this tool checks.
Scope of this check
A pass here confirms the 14 digits are internally consistent by the standard Luhn rule; it doesn’t confirm INSEE ever assigned that number, or that the establishment is still open. For that, check INSEE’s Sirene directory via annuaire-entreprises.data.gouv.fr, the same registry that issues both SIREN and SIRET numbers.
Content last reviewed 2026-07-22.
SIRET FAQ
What do the last 5 digits of a SIRET represent?
They're the NIC (Numéro Interne de Classement), a sequential code INSEE assigns to distinguish each physical establishment of a business from its others. A company with one head office and several branches has one SIREN shared by all of them, but each branch gets its own 5-digit NIC and therefore its own unique SIRET.
Why might a genuine SIRET fail this Luhn check?
One documented case: entities whose SIREN is 356000000 — most notably La Poste — use a SIRET checksum rule that departs from the standard Luhn calculation applied to every other French establishment. This tool, like most general-purpose validators, applies the standard rule and doesn't special-case that one exception.
Does every SIRET start with the business's SIREN?
Yes — the first 9 digits of a SIRET are always the same SIREN issued to the parent legal entity, and the next 5 digits are the NIC identifying that specific establishment. That's why two branches of the same company share the first 9 digits of their SIRET but differ in the last 5.