SIRET/SIREN Validator
ValidatorValidate French SIREN (9-digit) and SIRET (14-digit) business numbers instantly. Auto-detects which one you entered, checks the Luhn checksum, and applies the special La Poste exception. Free, runs in your browser.
Need to validate the matching VAT (TVA) number too?
This tool validates a French SIREN/SIRET. To validate the matching intracommunity VAT (TVA) number, use our TVA Validator →
About this tool
About SIRET/SIREN Validator
This validator checks French SIREN (9-digit) and SIRET (14-digit) business numbers, auto-detecting which one you entered. Ordinary numbers use the standard Luhn checksum; SIRETs under SIREN 356000000 (La Poste) use a special rule instead — the sum of all 14 digits must be a multiple of 5 — except for the head office number itself, which is hardcoded to standard Luhn.
Paste a 9-digit or 14-digit number and the tool detects which type it is, extracts the SIREN (and NIC, for a SIRET), reports which checksum algorithm applies, and confirms whether it passes. The embedded SIREN is independently re-checked with its own Luhn validation in every case, matching the reference behaviour used by widely-used open-source SIRET validators.
Use this validator to verify a SIREN or SIRET collected from a customer or supplier before storing it, to debug why a number is being rejected by another system, to check an invoice or KYB document for a typo, or to learn how the Luhn checksum and the La Poste exception work.
Instant validation with no network requests — everything runs locally in your browser. The tool clearly reports which algorithm was applied, which matters for the La Poste family of numbers where the rule genuinely differs from every other SIREN in France.
Key Features
- Auto-detects SIREN (9 digits) vs SIRET (14 digits)
- Standard Luhn checksum for ordinary companies
- La Poste mod-5 exception, including its hardcoded head-office carve-out
- Extracts and displays the SIREN and NIC from a SIRET
- Reports exactly which algorithm was used
- 100% browser-based, no data sent
FAQ
SIRET/SIREN Validator — Frequently Asked Questions
How does this validator know if I entered a SIREN or a SIRET?
It simply checks the length after stripping spaces, dots, and hyphens: 9 digits is treated as a SIREN, 14 digits as a SIRET. Any other length is rejected as invalid.
What does 'La Poste exception' mean in the result?
Any SIRET whose first 9 digits are 356000000 belongs to La Poste. Because most of its ~13,000 establishment numbers cannot satisfy the standard Luhn checksum, they are instead validated with a simpler rule: the sum of all 14 digits must be a multiple of 5. One specific number — the head office SIRET 356 000 000 00048 — is a documented, hardcoded exception to that exception, and is validated with standard Luhn instead.
Why did my SIRET fail even though the SIREN part looks right?
The 14-digit SIRET has its own checksum computed over all 14 digits — it is not simply 'a valid SIREN plus any establishment number'. The final digit of the NIC must be chosen so the whole 14-digit number satisfies the Luhn formula (or, for La Poste, the mod-5 rule). This tool always re-checks the embedded SIREN's own Luhn validity too, since a SIRET built on an invalid SIREN cannot be genuine.
Can this tool confirm a SIRET belongs to a real, currently active business?
No. This is a mathematical structure check only. A number can be checksum-valid without being currently registered, or a business could have closed after the number was issued. To check current registration status, use France's official Sirene directory (annuaire-entreprises.data.gouv.fr).
Tips
- Spaces, dots, and hyphens are stripped automatically before validation
- 9 digits = SIREN, 14 digits = SIRET — no need to specify which
- SIRETs starting with 356000000 belong to La Poste and use the mod-5 rule
- Use the SIRET/SIREN Generator on this site to create valid test numbers
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