FREE TOOL · NOTHING IS UPLOADED

Free G-code viewer

Look at a G-code program before you run it. Drop the file in and you get the toolpath in 3D, with rapid moves and cutting moves in different colours, plus the travel limits in every axis.

Drop a G-code file hereor click to choose one from your computerAccepts .nc, .gcode, .tap, .ngc and similar. Read in this browser, never uploaded.
Rapid (G0) Cutting move

What this viewer shows you

Drop a program in and you get the toolpath drawn in 3D. Rapid moves are drawn in a faded copper and cutting moves in near-black, which is the quickest way to spot the mistake everyone worries about, a rapid that goes straight through the part or the fixture.

You also get the travel in each axis, so you can check the program fits inside your machine and inside your workholding before you cut anything.

What it reads

  • Straight moves, both rapid and feed, meaning G0 and G1.
  • Arcs, meaning G2 and G3, using I, J and K centre offsets, including helical moves where the tool spirals down while it goes round.
  • Arc planes, meaning G17, G18 and G19, so arcs cut in XZ or YZ come out right rather than flattened.
  • Inch and millimetre programs, meaning G20 and G21, converted to millimetres for display.
  • Absolute and incremental positioning, meaning G90 and G91.
  • Feed rates, spindle speeds and tool numbers, which are reported so you can sanity check them at a glance.

What it does not do

This is a viewer, not a simulator, and the difference matters. It draws where the tool centre goes. It does not know your tool diameter, it does not remove material, and it will not tell you that you are about to crash into a vise it cannot see. Canned cycles such as G81 drilling are not expanded into their individual moves, and cutter compensation is not applied.

Treat it as a fast way to see the shape of a program and catch obvious problems. It does not replace running the program above the part with the spindle off, and it does not replace a proper machine simulation.

File formats

G-code goes by a lot of extensions depending on who wrote the post processor. This viewer accepts .nc, .gcode, .tap, .ngc, .cnc, .mpf, .eia and plain .txt. Comments in either parentheses or after a semicolon are ignored, as are line numbers and block delete slashes.

Questions

Is my program uploaded anywhere?
No. The file is parsed in your browser and never sent anywhere, which matters because a program can tell someone a great deal about the part you are making.
Which controls does it support?
It reads the common motion words that nearly every control shares, which covers most output from Fusion, Mastercam and similar. Control specific extras such as canned cycles and macros are skipped rather than guessed at.
Why are some moves missing?
Most likely they are inside a canned cycle such as G81 or G83, which this viewer does not expand into individual moves. Subprogram calls are also not followed.
Does it check for crashes?
No. It draws where the tool centre travels. It does not know your tool, your stock or your fixture, so it cannot tell you that a move is unsafe. Use it to catch obvious problems, not to certify a program.
What do the colours mean?
Faded copper is rapid traverse, meaning G0, and near-black is a cutting move at feed rate. A rapid that passes through where your part should be is the thing to look for.

Other free tools

STEP File ViewerOpen a STEP file in your browser and read its dimensions.STEP to STL ConverterTurn a STEP file into an STL you can slice and print.STL to STEP ConverterTurn a mesh into a STEP solid that CAD will open.Fixture plate generatorDescribe a part and an operation, and get a printable workholding fixture.

We build tools like this into the shops we work with, wired to their own machines, their own material data and their own systems. If that sounds useful, tell us what you run.

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