The decode's frequency in hertz above the dial frequency
The perceived clock differential between the local station and remote station, in seconds.
WSJT-X client name
The message payload contained in the decode
The protocol of the decoded message
Whether the decode is new or replayed
Whether the decode came from playback of a recording
Local station's perceived signal to noise ratio
Clock time in milliseconds since midnight
The decode message is sent when a new decode is completed, in this case the 'New' field is true. It is also used in response to a "Replay" message where each old decode in the "Band activity" window, that has not been erased, is sent in order as a one of these messages with the 'New' field set to false.
See WSJT-X source.