This OnixS reference article summarises FIX session-level and application-level message types (MsgType), FIX field tags, tag values and data types, and repeating fields field order and the message checksum (tag 10).
It is written as a useful reference for those who need to quickly understand the basics of FIX message structures.
FIX Protocol messages are a sequence of fields whose values are associated with numeric keys (tags).
All FIX messages begin with the field (e.g., 8=FIX.4.2) and terminate with the CheckSum field (e.g., 10=218). Each message field (tag and value pair) within these fields has a unique meaning.
The article includes further references to more detailed information on the FIX Protocol Dictionary that explains message types, tags, enumerations, mandatory/optional and conditional fields, and repeating groups.
Further useful technical references to programming guides for FIX message parser implementations in C++, .NET and Java are also included in the footer of this article.