GS1-128 Parser

What is a GS1-128 barcode?

A GS1-128 is a Code 128 barcode carrying structured data defined by GS1. On its own, Code 128 is just a way of encoding arbitrary text into bars and spaces. What makes a Code 128 barcode a GS1-128 is the FNC1 character at the start, which tells downstream software: the bytes that follow are a stream of GS1 Application Identifiers and their values, not free-form text.

You see them on logistic labels (pallet tags, carton labels), pharmaceutical packaging, and fresh-food weigh tickets. One symbol can pack a GTIN, a batch number, an expiration date, a serial number, a net weight, and a shipping container code all at once. That density is why GS1-128 has been the logistics workhorse since the 1990s.

The parser on this page doesn’t care whether you pasted a raw GS1-128 scan, a human-readable paren string off a label, or a GS1 Digital Link URL: it normalises all three into the same AI breakdown and lets you export to whichever form you need next.

Application Identifiers, in one page

An Application Identifier is a two-, three-, or four-digit code that prefixes a value and tells you what the value means. AI (01) always means “the next 14 digits are a GTIN”. AI (17) always means “the next 6 digits are an expiration date in YYMMDD format”. AI (10) means “what follows is a batch number, up to 20 alphanumeric characters, terminated when you hit the next FNC1”. Every AI is documented in the GS1 General Specifications, and once you internalise half a dozen common ones you can read most GS1-128 labels at sight.

The categories group naturally. Identification AIs like (01) GTIN, (00) SSCC, and (02) contained GTIN are primary keys for trade items and logistic units. Traceability AIs like (10) batch and (21) serial attach per-unit provenance. Dates — production, best-before, sell-by, expiry — all share the 6-digit YYMMDD format. Measurementsin the 3xxx range encode weight, length, and volume with an implicit decimal place determined by the last digit of the AI itself (so (3103) means “net weight in kilograms with 3 decimals”). LogisticsAIs like (400) purchase order and (410)–(417) GLNs identify parties and shipments.

Try editing the example below. Click any segment to see its full definition — name, format rule, help text, a real example, and validation errors if the value doesn’t conform.

Fixed vs variable length, and why FNC1 exists

The most common first question about GS1-128 is: how does a scanner know where one AI ends and the next begins? The answer depends on the AI. Fixed-length AIs — the ones where the General Specifications defines an exact byte count — need no separator. AI (01) is always 14 digits, AI (17) is always 6. As soon as the parser reads the code, it knows exactly how many bytes to grab.

Variable-length AIs are the problem. AI (10) batch can be anywhere from 1 to 20 characters. When it appears in the middle of a string, the parser doesn’t know where to stop reading the batch number and start reading the next AI. GS1 solves this with the FNC1 function character (ASCII 29, invisible in the printed label but included in the barcode encoding). Variable AIs that aren’t at the end of the string MUST be terminated by an FNC1. The parser here accepts both the raw FNC1 byte and the human-readable ]C1 symbology identifier that some scanners emit as a prefix.

Where you see them in the wild

GS1-128 shows up anywhere a single item carries more context than just a GTIN. A few places you’ve probably already scanned them without noticing.

Logistic labels (GS1-128 is the label standard)

Every pallet shipped between trading partners in Europe or North America carries an SSCC label, and the SSCC itself is AI (00). The same label often carries a GTIN-14, a batch, a best-before date, and a GLN of the destination. If you’ve ever received goods at a warehouse dock, you’ve seen GS1-128.

Pharmaceutical serialisation

Under the EU Falsified Medicines Directive and the US DSCSA, every prescription drug pack carries a 2D Data Matrix encoding (01) GTIN, (17) expiry, (10) batch, and (21) serial. That’s four AIs in one symbol, every one of them critical for anti- counterfeiting and recall traceability. Parse any of those codes here and you’ll see the full chain.

Fresh food and weight-variable items

Chicken breast packs at the supermarket, deli cheese wedges, butcher weigh tickets — anything sold by weight carries a variable-count AI (30), a net weight in the 31xx range, and usually a sell-by date (16). The cash register reads the GTIN, looks up the price per kilogram, and multiplies by the encoded weight. Without GS1-128, that workflow doesn’t exist.

Fishery and food traceability

Seafood carries a cluster of traceability AIs in the 7xxx range: (7005) catch area, (7006) first freeze date, (7008) species, (7009) fishing gear type. Regulators in the EU and several Asian markets require these to be scannable so the fish can be traced from catch to consumer. Paste a real seafood label and every one of these gets decoded.

Decoding pitfalls and common errors

A well-formed GS1-128 is unambiguous, but labels in the wild are rarely pristine. Here are the things the parser catches and the things it deliberately doesn’t.

• Wrong GTIN check digit. The parser runs the mod-10 algorithm on every AI (01) and (02) and flags a mismatch with the expected digit right in the breakdown card. This is the most common real-world error and the one that matters most for downstream systems.
• Dates that aren’t valid YYMMDD.Months must be 01–12, days 00–31 (00 meaning the day is unknown, which GS1 allows). An expiry of (17)260230 would parse structurally but fail the YYMMDD check.
• Missing FNC1 on a variable-length AI mid-string. Without the separator, the parser can’t tell where the variable AI ends. It’ll over-consume into the next AI and produce garbage. The fix is always on the encoding side, not the parsing side.
• Unknown AI codes.If the parser doesn’t recognise an AI code, it flags the card as “Unknown” and shows the raw bytes. This happens most often with company-internal 9x AIs that are scope-limited to bilateral agreements.

What the parser doesn’tcatch is semantic correctness: if your GTIN is valid but points at the wrong product, the tool can’t know that. For cross-referencing against a product master, use the output of this parser as input to your PIM or ERP.

Frequently asked questions