Check digit validator
Is this VIN well-formed?
Position 9 of a VIN is a checksum computed from the other sixteen characters. It catches most typos. This runs entirely in your browser — nothing is sent anywhere.
What a failed check digit does and does not mean
A failure is a warning, not a verdict.
A mismatch usually means a transcription error — a character misread off a windshield plate, or a digit transposed. Re-reading the VIN fixes most of them.
But the check digit is only mandatory for vehicles built for the North American market. Vehicles manufactured for other markets are not required to carry a valid one, so a grey import can fail this test and still be a perfectly genuine VIN.
A valid check digit also does not mean the VIN belongs to a real vehicle. It means the seventeen characters are internally consistent. Decode it to find out whether a vehicle exists behind it.
Algorithm defined in 49 CFR 565. See how the check digit works.