KIX Code (Royal TPG Post / PostNL)

KIX Code is the four-state postal barcode developed by Royal TPG Post (now PostNL) for encoding Dutch postal codes and house numbers on mail, notable for its deliberately minimal design: no start/stop characters and no check digit at all, trusting print quality and sorting equipment tolerance instead of built-in validation.

Most postal and logistics barcodes on this site — POSTNET, the USPS Intelligent Mail Barcode, Royal Mail's RM4SCC, Japan Post's 4-state barcode — include at least a checksum or check digit to catch scanning and printing errors before a piece of mail is misrouted. KIX Code, developed for the Dutch postal market, intentionally omits this: there is no check digit, and there are no distinct start or stop patterns framing the code. The barcode simply begins and ends with its data content, relying entirely on the fixed field structure (Dutch postal codes and house numbers follow a very regular, predictable format) and on the sorting equipment's ability to detect the barcode's boundaries from its bar pattern alone.

Like the Royal Mail RM4SCC and other modern postal codes covered elsewhere on this site, KIX Code uses four bar states rather than a simple binary bar/space pattern: each bar can be full-height, ascending only, descending only, or a short tracker bar, relative to a baseline. This lets each bar position carry more than one bit of information, allowing the Dutch postal code (four digits plus two letters) and house number to be encoded compactly enough to fit within the limited space available on a standard envelope, typically printed in the address block area alongside or near the printed address itself.

• The Dutch postal code (postcode), consisting of four digits followed by two letters, uniquely identifying a small geographic area, often down to a specific block or building.
• The house number and, where relevant, a house number addition/suffix, to pinpoint the exact address within the postal code area.
• No check digit — validation of correctness relies on downstream address-matching logic rather than the barcode's own structure.

KIX Code shares its four-state height-modulation concept with the USPS Intelligent Mail Barcode, Japan Post's customer barcode, and Royal Mail's RM4SCC, all covered elsewhere on this site, but stands apart from all of them by omitting both a check digit and start/stop framing — a minimalism made possible because the Dutch postal code system is dense and highly structured, letting sorting software validate plausibility against known postal code ranges rather than relying on an in-barcode checksum. This makes KIX Code one of the simplest postal barcodes to generate, at the cost of having no built-in mechanism to catch a misread or misprinted symbol before it reaches downstream address-matching logic.

Because KIX Code carries no error detection of its own, print quality and consistent bar placement matter more than they might for a checksummed alternative — a partially misread bar can silently produce an incorrect but plausible-looking postal code or house number rather than triggering an obvious validation failure. Businesses and mailing software generating KIX Code for Dutch mail typically rely on PostNL-published technical specifications and certified address-database software to ensure the encoded postcode and house number are correct at the source, since the barcode itself will not catch an error introduced before printing.