Technical SEO / E-commerce
GTIN, UPC, EAN & ISBN Checksum Validator
Paste your product barcodes or book ISBNs, one per line can already. We recompute every check digit using the real GTIN (mod-10) and ISBN-10 (mod-11) algorithm, and flag anything Google Merchant Center or a Product rich result confirm will reject one.
You can paste bare codes, codes with "ISBN"/"UPC"/"EAN"/"GTIN" in front, codes with spaces or dashes, or spreadsheet export like "SKU-1042, 9780306406157" — the label before the last comma or tab kept for your reference only, not checked one.
What this tool check
Every GTIN, UPC, EAN and ISBN got a check digit at the end, calculated from the digits before it. One typo or swapped digit anywhere already changes that check digit — that is exactly how Google Merchant Center, POS scanner, and library system catch bad codes automatically one. This tool run the same maths so you catch it first.
How the check work
Nothing here confirm guess one — each code classified by its length, then validated against its real published check-digit algorithm.
GTIN family (mod-10): EAN-8, UPC-A, EAN-13, GTIN-14
The GTIN.org / GS1 algorithm: start from the digit just left of the check digit, alternate weight 3 and 1, sum everything up, and check digit is whatever number make the total a multiple of 10. Covers 8, 12, 13, 14-digit codes with one formula only.
ISBN-10 (mod-11)
Different, older algorithm, only for 10-digit ISBN: the first 9 digits weighted 10 down to 2, sum up, and remainder mod 11 give the check digit — remainder 10 written as letter X, not two-digit number.
Duplicate detection
Same code appearing twice in one batch flagged separately from validity — duplicate GTIN across two different products is one of the most common reason Google Merchant Center suspend listing, even when both codes individually pass checksum.
Why this matter for SEO & Merchant Center
Schema.org Product markup (gtin8/gtin12/gtin13/gtin14/isbn) and Google Merchant Center feed both validated against these same check-digit rules — invalid code silently rejected or flagged as data-quality issue, can block Product rich results and shopping ads sia.
Frequently asked questions
What is "check digit" and why one wrong digit matter so much?
It is the last digit of a barcode or ISBN, calculated from every digit before it. If any one digit mistyped, duplicated, or swap with neighbour, the check digit almost never match anymore — that is why scanner and Google Merchant Center use it to catch data-entry error automatically.
My 13-digit code pass as EAN-13, but I thought confirm ISBN. How come?
ISBN-13 codes are, mathematically, just ordinary EAN-13 codes reserved in "Bookland" range 978 and 979 — checksum maths identical one. This tool label a 13-digit code as ISBN-13 automatically when it start with 978 or 979, and generic EAN-13/GTIN-13 otherwise.
Can this tool tell me the correct check digit for a code that fail?
Can — for any code with valid length whose check digit don't match, the result table show both the digit you key in and the one algorithm actually compute, so you see exactly what to fix.
This tool support UPC-E (compressed 6-8 digit code) anot?
Not yet — UPC-E need to expand back to full 12-digit UPC-A form before checksum apply, different process from validating a code that already carry its own check digit. Expand to UPC-A first, then paste the 12-digit result here can already.