Barcode Generator

Match the symbology to whoever is scanning it. CODE128 handles letters, digits and punctuation, and is the usual choice for anything internal — asset tags, bin labels, job numbers. CODE39 is older and produces a wider symbol for the same data, but some legacy systems still ask for it by name. EAN-13 and UPC-A belong at retail checkouts and nowhere else. ITF-14 goes on outer cases and cartons rather than on the retail unit inside them. MSI turns up in shelf labelling and stock control, and pharmacode is a packing-line mark read by machine vision rather than by a handheld scanner. If nobody has specified one, use CODE128.

For retail, yes — and what you are buying is the number, not the picture. Retail codes are allocated through GS1, which issues a company prefix; the digits after it identify your individual products, and the retailer's system looks the whole number up in a database that expects it to belong to you. Any generator, this one included, draws bars for whatever you type and has no way of knowing whether the number is yours. Inside your own operation there is nothing to buy at all: warehouse, library, workshop and asset codes are yours to invent, which is the case CODE128 exists for.

The final digit of a retail code is calculated from the digits before it by a weighted sum, so most numbers of the right length are not valid codes. Type thirteen digits for EAN-13 with a wrong last one and it fails even though the count looks correct. The format list accepts twelve digits as well as thirteen, which spares you the arithmetic — enter the twelve you were given and the last is derived from them. One thing to know when it does go wrong here: the message always ends with a nudge about digit count whatever the real cause was, so read it as a general this value will not encode in this format.

Four causes cover nearly all of it. The quiet zone, meaning the plain margin at each end of the symbol, has been cropped or crowded by a border or a fold — the image carries a fixed twelve-pixel margin, so add space around it in your layout rather than trimming in. Contrast is wrong: bars need to be dark on a light background, and red ink is close to invisible to a red-light scanner. The print is too small, or has been scaled up from a small image until the edges have gone soft. Or the label sits on a curve, under gloss, or wrapped round a corner.

UPC-A is twelve digits and grew up in North America; EAN-13 is thirteen and is the international form. They are closer than they look — an EAN-13 beginning with a zero is a UPC-A with that leading zero written out, and the bar patterns line up accordingly. Scanners sold in the last couple of decades read both without being told which they are looking at, so the choice is really about the form your number was issued in. Use that form rather than converting between them yourself, since the check digit is calculated over the digits as issued and a hand conversion is an easy thing to get wrong.

Not one of these. Every format on offer is linear, meaning the data runs in a single dimension, so capacity is width and a web address becomes a symbol far too wide to print or scan sensibly. CODE128 will accept arbitrary text, which is not the same as that being a good idea: the image grows with every character, and the bars get relatively narrower against the label around them. Anything longer than a short identifier belongs in a two-dimensional symbology such as QR or Data Matrix, which stack data in both directions and are what phone cameras are built to read.

Not here. There is one content field, one image and one download, so a hundred labels means a hundred passes by hand. Two things to watch if you do that: the image redraws the moment you type and replaces what was there, so save each one before starting the next, and the file is named after the format rather than the value, so every CODE128 download arrives as barcode-code128.png and your browser will start appending numbers to tell them apart. Rename as you go. For a genuine print run, a label program with mail-merge, or a barcode font applied to a spreadsheet column, is the right tool.

No. The barcode is drawn by a library loaded into the page, onto a canvas element that stays hidden, and the picture you see is that canvas read back as a base64 PNG. The Download PNG link points at that same string, so the file is assembled inside your browser and no image is requested from or written to a server. Nothing is kept between visits either: the content, format and height live in the page while it is open and go when you close the tab. That matters more than it sounds for a barcode, since what people encode is often an order number, a serial or an internal asset ID.