01Is my inventory/SKU data uploaded anywhere?
No. LabelStack runs entirely in your browser. CSV files, product names, SKUs, FNSKUs, and generated barcodes are parsed, validated, and rendered on your device. Nothing is posted to a server — there is no account and no backend that could store your catalog. You can confirm this in the network panel: generating and exporting never sends your rows anywhere. That is the point of the tool. Sellers who currently paste inventory into hosted generators are handing over supplier lists and Amazon FNSKUs; this site is built so we never see them.
02What label sheet sizes are supported?
Presets include Avery 5160 (1" × 2.625", 30-up), Avery 5163 (2" × 4", 10-up), Avery 5167 (0.5" × 1.75", 80-up), plus 5161, 5162, 5164, 8160, Amazon FBA 30-up and 2×3 in, and A4 sizes L7160, L7163, and L7651. Each preset uses the published page size, label size, margins, and gutters so a desktop laser or inkjet lands on the actual sticker grid. If you use a house brand or a European size that is not listed, choose Custom size and enter width, height, columns, rows, and margins in inches. Letter vs A4 is a different page box — read the paper-size guide before printing a US PDF on A4 stock.
03Is there a limit on how many barcodes I can generate?
No. There is no row cap, no page cap, and no watermark on PDF or ZIP exports. The only limit is your browser’s memory. Thousands of rows are parsed in chunks so the tab stays responsive; the sheet preview shows one page at a time while export walks the full set. If you generate tens of thousands of labels, leave the tab open until the PDF or ZIP finishes — it still never leaves your machine.
04Why is this free?
LabelStack is a client-side tool with no servers to rent for your data. Optional advertisements on the page (never on the PDF, never over the download button) are how the lights stay on once the publisher network accepts the site. There is no paid tier because the product is the browser app: generate, layout, export. If ads are blocked, the generator still works. We also publish original guides because a tool without the print-alignment and symbology context is how people reprint a hundred bad stickers.
05Do I still need to buy UPC or EAN numbers from GS1?
Yes, if you are selling at retail. This generator encodes the digits you already own. It does not issue GS1 company prefixes, UPC numbers, or Amazon barcodes. Enter licensed GTINs, or use Code 128 / FNSKU for internal and FBA labels. A 12-digit string with a valid check digit is not “your UPC.” Read the guide on why you should not invent UPC numbers.
06How do check digits work here?
EAN-13, EAN-8, UPC-A, UPC-E, and ITF-14 carry a GS1 modulo-10 check digit. LabelStack computes it from the payload, compares it to what you entered, and flags the spreadsheet row if they disagree — including the expected digit so you can fix one typo instead of reprinting a hundred labels. You can apply the suggested check digit in one click. Code 128, Code 39, and FNSKU do not use a GS1 check digit; those are validated for character set and length instead. Worked examples (including EAN-13 4006381333931) are in the check-digit guide.
07Why don’t my printed labels line up with the sheet?
Most desktop printers apply a small unprintable margin and may scale the page. Export the PDF at 100% scale, disable “fit to page,” and use the actual paper size (Letter or A4) in the print dialog. If everything is shifted the same amount, use the X/Y offset sliders in thousandths of an inch — that offset is applied to every label on every page. If you printed a Letter 5160 PDF on A4 paper, no offset will save you; match the paper to the preset. The Avery 5160 alignment guide walks through Chrome, Adobe, and macOS Preview settings.
08Who runs LabelStack?
LabelStack is an independent web app, not a product of Amazon, Avery, or GS1. The editors write the guides and maintain the generator. There is no account system. Reach us at contact@labelstack.app — do not email inventory CSVs. See the About and Contact pages for editorial standards and what we will not do.
09Can I use this for retail UPC/EAN if I bought numbers from GS1?
Yes. Encode the GTIN you licensed. The generator validates the modulo-10 check digit and will flag a typo before print. It does not sell prefixes. If you do not own the number, do not print it as a retail barcode; use Code 128 for internal SKUs instead.
10Where can I learn FNSKU vs UPC vs Code 128?
Read the Code 128 vs UPC vs EAN vs FNSKU guide and the Amazon FBA FNSKU labels guide. Short version: cashiers want a licensed UPC/EAN; Amazon inbound wants an X-prefixed Code 128 FNSKU; bins and house SKUs want Code 128. Mixing them on the same physical unit is how inventory strands.
11Does LabelStack print postage or Amazon’s own shipment PDF?
No. Carrier postage (USPS, Etsy shipping, Pirate Ship, and the rest) is a paid label with a tracking barcode you must not redesign. Amazon’s required shipment PDFs should be used when Seller Central says so. This site reprints product, FNSKU, SKU, bin, and GTIN stickers from your own file.
12Should I use laser or inkjet for Avery barcode sheets?
Match the wrapper to the machine: 5160 is typically laser, 8160 typically inkjet. Use 100% black, not a photo-driver composite. Cheap toner that prints grey bars will fail a warehouse gun even if a phone camera beeps. Details in the laser vs inkjet guide.
13Can I print ISBN-13 for books?
Yes. ISBN-13 is EAN-13 with prefix 978 or 979. Strip hyphens, set symbology to ean13. ISBN-10 is not an EAN; convert first. This tool does not print the five-digit bookland price add-on. See the ISBN-13 guide.
14How should I test a sheet before a full run?
Print one page on the real stock at 100% scale. Scan top-left, center, and bottom-right. A phone pass plus a warehouse-gun fail is a fail. Read the decoded value against the spreadsheet, not just the beep. Protocol: the test-scan guide.