Check a French social security number

Paste a French social security number as printed on a pay slip or a certificate: the tool recomputes its two-digit key and decodes what the first 13 digits say. This is personal data: everything is computed in your browser and the number is not sent anywhere.

The calculation runs in your browser: the number you type is not sent to any server.

What this check proves

That the number is well-formed. The last two digits are a key computed from the other thirteen: 97 minus the remainder of their division by 97 — for Corsica, 2A counts as 19 and 2B as 18. A miscopied digit, two swapped digits or a number typed at random fail in almost every case.

What it does not prove

That the number was ever assigned, or that it belongs to the person named on the document. The national register (RNIPP, kept by INSEE) is not open to the public; only social-protection bodies and, through payroll declarations, employers can query it. Fake pay-slip generators compute a correct key, so a valid key is no authentication. The other signals in the pay-slip guide are what make the difference.

How to read the number

• 1st digit: sex (1 male, 2 female). 3, 4, 7 or 8 mark a provisional number.
• Digits 2 to 5: year then month of birth. A month of 20, or 30 to 99, means an incomplete date or a special case, not an error.
• Digits 6 and 7: département of birth (2A or 2B for Corsica, 99 for a birth abroad — the next three digits then give the country).
• Digits 8 to 10: municipality (or country), then 11 to 13: order number in the register.
• Key: the last two digits, recomputed here.

Cross-check with the document

On a pay slip, the decoded sex and birth year must match the person; a "female" number on a man's pay slip, or a birth year incompatible with the stated age, betrays a template filled in a hurry. The number must also be identical from one pay slip to the next and on the employer's certificate.

Check the whole pay slip, not just the number

TrustyFile examines the PDF as a whole: successive revisions, covered text, inconsistent fonts, online-generator metadata, arithmetic consistency. A modern fake pay slip almost always has a valid NIR key — and almost always one of these other defects.

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