FIX message structure

A FIX message consists of a header, a message body, and a trailer:

  • Header - The FIX message header identifies the message type, length, sender/destination, sequence number, sending time etc.
  • Body - The FIX message body contains specific session and application message content.
  • Trailer - The FIX message trailer contains an optional digital signature and the required checksum value.
It should be noted that all fields within the message can be defined in any sequence with the following exceptions:
  • tag number 8, 9, and 35 of the header block must be the first three fields in the message
  • tag number 10 of the trailer block must be the last field in the message
  • fields within a repeating block must appear in the same order as defined in the FIX standard documents
  • the number of repeating group instances must immediately precede the repeating group contents
  • binary fields must be preceded by corresponding length fields