Practical scope and examples
Use the original digits
Enter a GTIN as text, including every leading zero. For example, 036000291452 is a 12-digit example with a valid check digit. Spaces, hyphens, non-ASCII digits and scientific notation are rejected by this focused tool. If a spreadsheet has already removed digits, recover them from the actual manufacturer record.
What the calculation means
The check uses alternating weights of three and one, starting from the right of the data digits. The final digit completes the sum to a multiple of ten. This helps detect many transcription errors; it is not proof that a manufacturer assigned the number to your product.
A valid checksum has limits
This tool does not query GS1, establish ownership, verify brand allocation or guarantee acceptance by Google. Restricted prefixes and destination-specific rules need separate review. Do not change an authentic manufacturer barcode merely to make a checksum pass.
Check a whole catalog
For a CSV, XLSX or supported XML catalog, use the main FeedDoctor analyzer. It preserves identifiers as text, flags duplicate product IDs and relates findings to product rows. Product IDs and GTINs are different attributes. Neither should be silently replaced with a newly generated number.