How to Fix Invalid Barcodes and Generate Missing SKUs

A surprising number of failed marketplace feed uploads and blocked product imports come down to two boring root causes: a barcode whose check digit doesn't actually validate, and a SKU column with blank cells scattered through it. Both are easy to introduce — a supplier feed truncates a digit, someone pastes a barcode from a spreadsheet that reformatted it, a batch of new products gets created without SKUs assigned yet — and both are tedious to find by eye in a file with thousands of rows.

The Barcode/EAN Validator & SKU Generator checks every barcode's check digit, flags duplicates, and fills in the blanks in one pass.

Why a "valid-looking" barcode can still be wrong

EAN-13, EAN-8, UPC-A and GTIN-14 codes all end in a check digit computed from the digits before it. A barcode can look completely normal — right number of digits, no stray characters — and still be invalid, because that last digit doesn't match what the rest of the code computes to. Marketplaces and POS systems that verify the check digit will reject or silently mis-scan these; ones that don't will happily import a code that never matches the product it's supposed to identify anywhere else in your supply chain.

Duplicate barcodes cause a quieter problem: two different products sharing one barcode confuses inventory sync, scanning at checkout, and any system that looks products up by barcode instead of SKU.

Quick check: paste a few codes without uploading anything

If you just need to sanity-check a handful of codes, paste one per line into the quick-check box at the top of the tool and click Check. Each one is validated instantly, with its detected type (EAN-13, EAN-8, UPC-A, ISBN-13 or GTIN-14) and, if the check digit is wrong, the corrected code right next to it. There's nothing to upload for this — it's meant for a fast spot-check, not a full catalog pass.

Batch mode: fix a whole catalog export

Step 1 — Upload your export

Upload the CSV or Excel export you'd normally send to a marketplace or re-import to your store. The tool auto-detects your barcode column (it recognizes headers like Barcode, GTIN, EAN or Barkod) and your SKU column, or lets you pick them manually if the guess is wrong.

Step 2 — Choose how corrections are applied

Two checkboxes control the behavior:

• Add a missing check digit — turn this on if some of your codes are one digit short (a common symptom of a spreadsheet that dropped a leading or trailing digit).
• Write corrected barcodes into the barcode column — on by default, this overwrites a wrong check digit with the corrected one. Turn it off if you'd rather review corrections in a separate column first and decide row by row.

Step 3 — Pick a SKU pattern for blank rows

Choose one of three ready-made patterns — a simple prefix and sequence number, a brand-and-category-based pattern, or one derived from the barcode itself — or, on Pro, write a custom template combining any column in your file with a sequence number. Only rows with a blank SKU are touched; anything you've already assigned is left exactly as it is. A live preview shows what the next few generated SKUs will look like before you run anything.

Step 4 — Run it and download

Click Check & Generate to get a summary — how many barcodes were valid, fixed, invalid, duplicated or empty, and how many SKUs were generated — then download the same file back with Barcode Status and Barcode Fixed columns added (and a new SKU column, if you didn't have one) and every blank SKU filled in.

A worked example

A 600-row product export has 12 barcodes with a wrong check digit (probably from a supplier who re-typed a few by hand), three barcodes that appear twice because two variants got assigned the same code by mistake, and 40 new products created without SKUs. Running the tool once produces: 12 corrected barcodes ready to overwrite the originals, the 6 duplicate rows flagged so you can assign the second one a real code, and 40 SKUs filled in using your chosen pattern — instead of finding all three problems separately by scrolling through the file.

Try it now

Open the Barcode/EAN Validator & SKU Generator and upload your export, or load the sample file to see every status at once — valid, fixed, duplicate and empty. If blank or inconsistent variant data is also part of your cleanup, running the Variant Value Cleaner over the same export first means you fix all of it before the next import instead of one problem at a time.