.GCODE File Format – Slicer comments

Identifying the producer

Readers look at the first comments for a producer string. PrusaSlicer’s own G-code reader recognises these:

PrusaSlicer

Header

After the producer line come optional ; prepared by and notes lines, then the thumbnails, then the extrusion widths used: ; external perimeters extrusion width = 0.45mm, and the same for perimeters, infill, solid infill, top infill, support material and first layer.

Markers in the body

Users’ own custom G-code must not contain the reserved tags, and PrusaSlicer warns when it does. Other comments starting ;_ (such as ;_EXTRUDE_SET_SPEED and ;_SET_FAN_SPEED) are internal markers that are removed before the file is written.

Feature roles

Statistics and progress

Near the end come lines such as ; filament used [mm] = , ; filament used [cm3] = , ; filament used [g] = , ; filament cost = (one value per extruder, comma separated), ; total filament used [g] = , ; total filament cost = , ; total filament used for wipe tower [g] = , ; total toolchanges = , ; estimated printing time (normal mode) = 1h 2m 3s, the same for silent mode, and ; estimated first layer printing time (normal mode) = . Through the file it inserts M73 Ppercent Rminutes left lines (Q and S for silent mode, C and D for minutes to the next colour change).

Settings block

The file ends with every setting, one per line, between ; prusaslicer_config = begin and ; prusaslicer_config = end, each line ; key = value. Recent versions can also write the settings as JSON between ; prusaslicer_json_config = begin and ; prusaslicer_json_config = end, each line of the JSON prefixed with ; . PrusaSlicer reloads its settings from this block when the G-code is opened.

Embedded thumbnails

PrusaSlicer (and the slicers that copy it) stores preview images in comments near the top, so a printer can show them. Each image is compressed, Base64 encoded and split over comment lines of at most 78 characters:

;
; thumbnail begin 16x16 1220
; iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAADW0lEQVQ4jW2TX2xTdRTHP/f+7u1u
; …
; thumbnail end
;

The sizes and formats come from the printer profile; Prusa’s own printers ask for several sizes. RepRapFirmware hands embedded thumbnails to its web interface with M36.1.

UltiMaker Cura

Flavours

Cura writes for one G-code flavour, chosen in the printer settings, and names it on the first line as ;FLAVOR:name: Marlin, Marlin(Volumetric), RepRap, UltiGCode, Griffin, Cheetah, Makerbot, BFB, Mach3 or Repetier.

Header

For most flavours the header is short:

The Griffin and Cheetah flavours (UltiMaker’s own printers) use a longer header between ;START_OF_HEADER and ;END_OF_HEADER, with ;HEADER_VERSION:0.1, ;FLAVOR:, ;GENERATOR.NAME:Cura_SteamEngine, ;GENERATOR.VERSION:, ;GENERATOR.BUILD_DATE:, ;TARGET_MACHINE.NAME:, and per extruder n ;EXTRUDER_TRAIN.n.INITIAL_TEMPERATURE:, .MATERIAL.VOLUME_USED:, .MATERIAL.GUID:, .NOZZLE.DIAMETER: and .NOZZLE.NAME:, then ;BUILD_PLATE.INITIAL_TEMPERATURE:, ;BUILD_VOLUME.TEMPERATURE:, ;PRINT.TIME:, ;PRINT.GROUPS:, ;PRINT.SIZE.MIN.X: to ;PRINT.SIZE.MAX.Z:, ;SLICE_UUID:, and print-process reporting limits (;PPR_ENABLE:TRUE and the PPR_ warning and limit values).

Markers in the body

Cura appends its settings at the very end on lines starting ;SETTING_3 , holding a JSON object of changed settings broken into short lines.

What is not covered

Other slicers (Simplify3D, ideaMaker, KISSlicer, Bambu Studio and OrcaSlicer’s own additions) have their own comment conventions that are not documented here.