FIX Tagvalue Encoding Standard

The FIX TagValue Encoding Standard is the formal technical specification for the original and still most widely used encoding of FIX messages. It defines how FIX messages are serialised into a byte stream by representing each field as a numeric tag, followed by an equals sign, followed by the field value, with each field separated by the Start of Heading control character. This was approved as a final FIX technical standard in June 2020. It later became recognised internationally as ISO 3531-1:2022.