Code 128 barcode generator

What this tool does, exactly

Code 128 is the barcode for everything that is yours: asset tags, shelf locations, order and batch numbers, membership cards. It carries letters, digits and punctuation at any length, needs no number issued by anyone, and every ordinary scanner reads it. The symbol is drawn with its check character and quiet zone in place.

What it holds

All 128 ASCII characters: capitals, lower case, digits, spaces and ordinary punctuation, with no fixed length. The symbol grows wider with every character, so a fifty-character code is a long strip. Anything outside ASCII, such as an accented letter or an em dash, is refused rather than swapped, because a scanner would then read something other than what you meant.

The three code sets

Code 128 switches internally between set A (capitals and control characters), set B (upper and lower case) and set C (pairs of digits packed into one symbol). The encoder here starts in whichever set makes the symbol shortest and switches mid-stream when that saves space, so a run of digits comes out at roughly half the width of the same digits as text.

The check character

Every Code 128 symbol ends in a check character, a weighted sum of everything before it, modulo 103. A scanner recomputes the sum on each read and rejects a mismatch, so a smudged bar produces no read rather than a wrong one. It is drawn for you; there is no Code 128 without it.

Text that is refused

Code 128 here carries ASCII only. If you type a character outside it, the tool names that character and stops, and tells you the letters A to Z and a to z, digits, spaces and ordinary punctuation are all fine.

Sizing a Code 128 label

There is no nominal size. What matters is the narrowest bar, which should be at least 0.19 mm for a handheld scanner and more for a fixed one, and a quiet zone of ten modules each side, which is drawn into the file. Scale proportionally, print black on white, and take the SVG for thermal printers.