The VIN is on the driver’s side of the dashboard, visible through the windshield, on the door-jamb sticker, and on your registration and insurance card. Type it in and the app looks it up in the public NHTSA database, which returns the year, make, model, trim, engine and body style.
If a VIN will not decode, check for a mistyped character: VINs never contain the letters I, O or Q, which are easy to confuse with digits.
What the VIN is used for
Parts, service intervals and the health score are all specific to the engine and trim, so the decoded profile is what every quote and recommendation starts from. Otopair also keeps a per-VIN record of what shops have physically confirmed about the car, such as mileage, tires, fluids, brakes and inspection status, with the date of the last shop confirmation. That record travels with the car, not with the owner.
If an Otopair shop has already serviced the car as a walk-in, the shop may have sent you a claim link by text or email; claiming it attaches those records to your account. If you decoded a VIN with Oto on the website and left your email, the car is attached automatically when you sign up with the same address. What is stored, and why, is on the privacy page.