G-code viewer

What to look for before you print

Drag the layer slider from the bottom to the top and watch the print build. It takes a minute and it catches most of the failures that would otherwise show up hours into a print.

Start with the first layer. Switch on "This layer only" and check that it covers the whole footprint of the part, with a skirt or brim around it if you asked for one. A first layer with gaps in it is the commonest reason a print comes loose.

Then look for anything printed in mid-air: a layer that starts with nothing under it. That is an overhang with no support, and it will droop or fail. Supports are drawn in green, so you can see whether the slicer put them where you expected — and nowhere you did not want them.

Finally switch on travel moves, drawn as thin blue lines. Travel that crosses a large gap in the part leaves strings; a lot of it on a single layer is worth fixing in the slicer with a different seam position or combing setting.

Reading the colours

Every current slicer labels what each line is part of, and the viewer uses those labels. The outer wall is orange, because it is the surface you will see. Inner walls are amber, infill is red, and top, bottom and other solid layers are violet. Supports are green, the skirt and brim are teal, and a prime tower is grey.

Each colour has a box beside it. Untick infill and the walls stand alone; untick supports and you see the part as it will be once they are removed.

Layers below the one you are on are drawn darker, and the current layer is drawn brighter, so the print reads as a solid object and the layer you are looking at stands out. A file with no labels — some older slicers and most hand-written G-code — is drawn in one colour.

How the print time is worked out

Adding up each move’s length divided by its speed gives a time that is far too short, because a printer spends most of a short move speeding up and slowing down. So every move is run through the same kind of planner a printer’s firmware uses, with the acceleration and speed limits the file itself sets, and timed as the move really runs.

Where the slicer wrote its own estimate into the file, it is shown beside ours. Trust the slicer’s number first: it simulated the firmware it was set up for. Ours is there for the files that state no estimate, and as a check — the two normally agree within about ten per cent.

Neither figure includes heating the bed and the nozzle, which adds a few minutes at the start, or any pause for a filament change.

Filament and weight

The filament figure is the length that actually went through the nozzle: every retraction is taken back off when the filament is pushed forward again. The weight uses the filament density the slicer wrote into the file, and assumes PLA when it wrote none.

To turn that into money — plastic, electricity, printer wear and failed prints — press "Work out what this print costs" and the same file opens in the cost calculator.

Files it opens

G-code from Cura, PrusaSlicer, OrcaSlicer, SuperSlicer, Bambu Studio, ideaMaker, Simplify3D and Creality Print, with the extensions .gcode, .gco and .g. It follows every setting that changes what a number means: absolute and relative extrusion, relative moves, a shifted origin, inches, and arcs, which PrusaSlicer, OrcaSlicer and Bambu Studio all write.

Bambu Studio and OrcaSlicer save a sliced plate as .gcode.3mf, which is a ZIP with the G-code inside. Drop that file in directly and the G-code is read out of it.

Binary G-code (.bgcode), which PrusaSlicer writes for the MK4, the MINI and the XL, cannot be opened yet. PrusaSlicer writes plain G-code for the same printers if you untick "Supports binary G-code" in Printer Settings.

Large files

The file is read in a background thread, so the page stays responsive while a fifty-megabyte print loads. Once it is open, every line is on the graphics card and the layer slider only changes how much of it is drawn, which is why dragging it is as smooth on a large print as on a small one.