Linting

Printers don't report mistakes. They quietly clamp values, ignore commands or never print a label. lint() finds these problems before you print.

import { parse, lint } from "node-zpl";

lint(parse("^XA^FO10,10^GB1,64,2^FS^FO40,40^BE^FD123^FS").commands);
// [
//   { rule: "box-smaller-than-line", severity: "warning", index: 2, span: { start: 11, end: 20 },
//     message: "The box is 1 dot wide but its line is 2 dots thick, so the printer widens it to 2 dots." },
//   { rule: "ean13-data", severity: "warning", ... },
//   { rule: "missing-end-format", severity: "error", ... },
// ]

Labels built with Label or JSX can be checked with label.lint(). Each problem has the command's index and, for parsed ZPL, its span in the text.

Errors stop the label from printing as intended. Warnings mean the printer will change something.

Media sizeCopy Anchor Link

Labels that don't set ^PW and ^LL take their size from the printer. Pass the media size in dots to check them too:

lint(commands, { width: 812, length: 406 });

RulesCopy Anchor Link

missing-start-formatCopy Anchor Link

Error. Commands come before the first ^XA. The printer ignores everything outside ^XA … ^XZ.

missing-end-formatCopy Anchor Link

Error. The label never ends with ^XZ, so the printer keeps waiting for the rest and nothing prints.

unclosed-fieldCopy Anchor Link

Error. A field started with ^FO or ^FT is never closed with ^FS, so it merges with the next field.

command-outside-formatCopy Anchor Link

Warning. A command comes after ^XZ and before the next ^XA, so the printer ignores it.

separator-without-fieldCopy Anchor Link

Warning. A ^FS has no ^FO or ^FT before it. Watch out for comments: a ^FX comment ends at the next ^, so ^FX close with ^FS contains a real ^FS.

field-outside-labelCopy Anchor Link

Warning. A field starts outside the label, so it may not print. A right-justified field can still reach into the label.

box-smaller-than-lineCopy Anchor Link

Warning. A box is narrower or shorter than its line thickness. The printer enlarges the box to the thickness.

value-out-of-rangeCopy Anchor Link

Warning. A value is outside what the printer accepts, for example a ^BY module width above 10. The printer clamps it or uses the default.

ean13-dataCopy Anchor Link

Warning. EAN-13 data must be exactly 12 digits; the printer adds the check digit. Other lengths are padded or cut, which prints a different barcode.

barcode-without-dataCopy Anchor Link

Warning. A barcode has no ^FD data, so nothing prints.

unknown-commandCopy Anchor Link

Warning. A command doesn't exist in ZPL, often a typo.