GS1-128 Parser

A variable-length element must be terminated by FNC1 (encoded as the GS character) unless it is the last element in the string. Without it there is no way to tell where the data ends and the next AI begins — the scanner reads the following AI as part of your batch number.

Fix: Insert a group separator after the variable-length field. In the human-readable form this is implicit; in the encoded data it must be a real FNC1.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

AIs whose length is predefined by their first two digits must NOT be followed by a separator. An extra FNC1 there is a common encoder bug and makes the string non-conformant.

Fix: Remove the separator after fixed-length elements such as (01), (17) and (00).

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

The string ends before this element has all the characters its AI requires.

Fix: Check that the barcode was scanned completely; a partial read usually means a damaged symbol.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

The data does not match the length its AI defines — fixed-length AIs need exactly that many characters, variable-length ones must not exceed their maximum.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

Numeric AIs accept digits only. Alphanumeric AIs use the GS1 AI character set — uppercase letters, digits and a limited set of symbols; lowercase letters are not permitted.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

GTIN, SSCC, GLN and GSIN values carry a GS1 Mod-10 check digit. A mismatch means the number is wrong, not merely formatted oddly.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

GS1 dates are YYMMDD. A day of 00 is legal and means "end of the month"; any other impossible date is an error.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

GS1 resolves a two-digit year to the range from 49 years before to 50 years after the current year. The same digits therefore mean different centuries depending on when they are read.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

This AI is not in the tool's table. GS1 adds AIs over time, so an unknown code is not automatically invalid — but without a definition we cannot tell how long its data should be, so parsing stops here.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.

Most AIs may appear only once in an element string. A repeat usually means two barcodes were concatenated.

Source: GS1 General Specifications — Application Identifier definitions and the table of predefined-length AIs. Rules verified against real GS1-128 element strings in our regression tests.