Barcode Generator

Overview

A barcode is not a handful of vertical lines drawn at random. Each symbology carries its own character set, structural rules and check algorithm, and a single wrong character makes a scanner return nothing. This generator covers five of the most used symbologies. Code 128 set B encodes the ninety-five printable ASCII characters and computes a mod 103 check symbol. Code 39 covers forty-three characters and needs the asterisk start and stop guards rather than a check digit. EAN-13 and UPC-A compute a mod 10 weighted check digit, and the parity pattern of the left half is dictated by the first digit. ITF-14 is the interleaved two of five code, packing fourteen digits in pairs. Entering twelve digits fills in the thirteenth check digit automatically, while entering a complete code first verifies the check digit and refuses to draw when it is wrong, telling you the value it should have been.

Features

• Five symbologies in one dropdown: Code 128 B, Code 39, EAN-13, UPC-A and ITF-14
• EAN-13 and UPC-A auto-complete the check digit from twelve or eleven digits and reject a wrong check digit with the correct value
• Code 128 computes its mod 103 check symbol and adds start and stop bars; Code 39 adds the asterisk guards and the inter-character gap
• Canvas renders at two, three or four pixels per module, with the width following the payload
• Four diagnostics per render: symbology, data length, module count and check information
• One-click PNG download named after the symbology, ready for a label template

How to use

1. Choose the symbology: EAN-13 for retail goods, UPC-A for North American retail, ITF-14 for cartons, Code 128 or Code 39 for internal numbering
2. Enter the data: twelve or thirteen digits for EAN-13, eleven or twelve for UPC-A, thirteen or fourteen for ITF-14
3. Set the module width to match the label, using two pixels for small thermal labels and three for ordinary forms
4. Check the four diagnostics and the canvas preview to confirm the check digit and module count
5. Download the PNG, or copy the final string including the computed check digit

Notes

• A wrong check digit is never drawn: the last digit of EAN-13 and UPC-A is derived from the earlier ones, so the tool validates before rendering
• Code 128 here is set B only, covering ASCII 32 to 126, which means Chinese characters, full-width punctuation and tabs are rejected and belong in a QR code instead
• Code 39 accepts only digits, upper-case letters and the symbols dash, dot, space, dollar, slash, plus and percent; lower case is outside the standard and is not silently upper-cased
• Resolution decides whether a scanner reads the symbol: below two pixels per module a laser scanner may misread, and thermal printing needs at least that plus quiet zones
• The first digit of EAN-13 sets the L and G parity of the left half, so changing it rewrites the entire symbol structure rather than just the number
• ITF-14 carton labels normally require a frame and bearer bars; this tool draws the bars alone, so add the frame in label software before production printing
• Quiet zones are included at ten modules on each side, which is the minimum most scanners expect