G-code Viewer
Open and preview G-code files online. 3D toolpath view with layer-by-layer slider, extrusion and travel moves, print statistics and model dimensions — no install, fully local.
What is a G-code viewer used for?
It shows what a 3D printer or CNC machine will actually do before you run the file: where the tool moves, which lines deposit material, how tall each layer is and how large the finished object will be. It is the fastest way to spot a failed slice, a wrong origin or a missing feature.
Which file formats and commands are supported?
Files with .gcode, .gco, .nc and .txt extensions work. The parser handles G0/G1 rapid and feed moves, G2/G3 arcs given as I/J center offsets or an R radius, G20/G21 inch/millimeter units, G90/G91 absolute/relative positioning, G92 position resets, and M82/M83 extruder modes. Other M codes are ignored safely.
How are extrusion and travel moves told apart?
Whenever the E value increases during a move, the segment is treated as extrusion and drawn in color. Moves without extrusion — hops, retraction gaps, returns — are travel moves, hidden by default and shown as faint gray lines when you enable the travel toggle.
What do the colors mean?
Extrusion lines are colored by layer height: the bottom layer is one color and the color shifts gradually toward the top, so you can see the print build up and spot layer problems at a glance.
What does the layer slider do?
It clips the view to the selected layer: dragging it down shows only the path up to that height, which is ideal for inspecting a specific feature. The geometry is rebuilt live while you drag.
What do the statistics mean?
You get the total number of lines in the file, the number of path segments produced, the X×Y×Z size of the printed object in millimeters, the number of distinct layers, and the estimated filament length consumed (the sum of all forward E movements).
Is my G-code uploaded to a server?
No. The file is parsed in a Web Worker inside your own browser and rendered locally. Nothing leaves your device, so you can safely preview proprietary or customer prints.
Can it handle very large files?
Yes. Parsing runs in a background thread with progress feedback, and files over 30 MB simply show a notice while they are still processed. Extremely large files may take a while and use a lot of memory, but they do work.
Why does the preview look empty or wrong?
Most cases are units or origin issues: a file in inches opened as millimeters looks huge, and models far from the origin can sit outside the initial view. Use the reset view button and check that G20/G21 units match your file. Files without any recognizable G0–G3 movement cannot be rendered.
How to Use G-code Viewer
This G-code viewer renders 3D printing and CNC toolpaths right in your browser. The file is parsed in a background worker that understands G0/G1 moves, G2/G3 arcs, inch/millimeter units, absolute and relative positioning and extrusion tracking, then the path is drawn with WebGL: extrusion colored by layer height and travel moves hidden until you want them. Nothing is uploaded — parsing and rendering are entirely local.
- Click the upload zone or drop a .gcode / .gco / .nc / .txt file onto it — parsing starts immediately and a line counter shows progress.
- Explore the 3D view by dragging to rotate, scrolling to zoom, and right-dragging to pan; the model sits Z-up just like on the printer.
- Use the layer slider to clip the view to a specific layer; drag it down to inspect lower features and back up to see the full print.
- Tick "Show travel moves" to reveal non-extruding moves as faint gray lines, useful for spotting wasteful hopping.
- Check the statistics row for total lines, path segments, the X×Y×Z size in mm, the layer count and the estimated filament length.
- If the view feels off, press "Reset view" to re-fit the camera to the whole model.
Colors run from cool at the first layer to warm at the last, so a quick scroll through the layer slider is the fastest way to sanity-check how a print builds up.
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