What you can check in a CNC file
- Rapids and feed moves. G0 moves are drawn as rapids and G1 moves as feed moves, so you can see where the tool travels quickly and where it works. Rapids that cross the part are worth a second look. The viewer cannot see your stock or clamps, so this is a visual check, not a collision check.
- Arcs. G2 and G3 arcs are drawn from I/J/K offsets or an R value in the active plane (G17, G18 or G19), including full circles and helixes.
- Extents. The bounds table shows the minimum and maximum X, Y and Z of the programmed path, which you can compare with your stock size and machine travel. Bounds describe where the tool moves, not the size of the finished part.
- Order of operations. Step through the movement sequence to watch the job in the order the controller will run it. Tool selections (T and M6) are recorded.
- Source lines. Click a path to jump to its line, or click a line to highlight its move.
How to view a CNC file
- Drop your file onto the upload area or choose it with the browse button.
- Check that the profile reads CNC / milling. It is detected from spindle commands (M3/M4), tool changes (M6) and CNC modal codes such as G40–G43, G54–G59 and G81–G89. If it is wrong, switch it manually; the profile only changes how moves are labeled and never alters your file.
- Use the 2D top view for the XY layout and the 3D view for depth.
- Play the movement sequence, and open the parser notes for anything the viewer skipped.
Set the Units selector to inches if your program uses G20 and the numbers look wrong. Layer controls belong to the 3D printing profile; CNC files are stepped through by movement.
What the viewer shows as programmed, and what it does not apply
| Feature in your file | What the viewer does |
|---|---|
| Work offsets G54–G59 | Treated as one shared coordinate system, with a note in the parser notes. Coordinates are shown as programmed. |
| Tool length offset G43 | Not applied. Programmed Z values are shown. |
| Cutter compensation G41/G42 | Not applied. The programmed path is shown. |
| Scaling or rotation G51/G68 | Not applied. A warning is listed because the real path may differ. |
| Canned cycles G81–G89 | Not expanded. A warning is listed, so drilled holes will not appear. |
| Splines (G5) and G30 | Not drawn. A warning is listed. |
Parameters and expressions (#100, [1+2]) | Those lines are skipped with a warning. |
| Rotary axes A, B, C | A, B and C words are ignored without a warning. A 4th- or 5th-axis program is drawn as if only X, Y and Z moved, so the result is not reliable for rotary work. |
| Feed moves | Labeled as feed moves, never as “cutting”, because a file alone cannot say whether the tool is in material. |
If holes are missing, many CAM post-processors can output drilling as plain moves instead of canned cycles; check your post-processor’s options.
Toolpath playback, not a machine simulation
If you are looking for a CNC simulator online, this plays the programmed path back move by move, but it is a viewer. It draws the path your file describes. It does not simulate material removal, machine limits, collisions, tool offsets or run time. Use it to check that a program looks right before you run it, and use your CAM or controller simulation for verification. Treat the result as a way to look, not a guarantee that a job is safe to run. More in G-code simulator online.
CNC G-code viewer questions
Does it estimate machining time? No. It reports statistics derived from the commands it understood and does not estimate time or material use.
Is my file uploaded? No. It is read and drawn in your browser. See the privacy policy.
Which files will open? Plain-text G-code up to about 150 MB. The picker suggests .gcode, .gco, .gc, .g, .nc, .tap, .cnc, .ngc and .txt, but any plain-text file with recognizable motion commands works. Not sure what an extension means? See the NC file viewer page or how to open .nc and other G-code files. If a file will not load, see the troubleshooting guide.
Back to the online G-code viewer.