G-code Viewer — Preview Print Toolpaths Online
Visualise the toolpath in a sliced .gcode file before you commit hours of printing to it.
Your G-code file is read and rendered entirely by your own browser. It is never uploaded to A23D, never stored, and never seen by anyone but you.
How to open a G-code file
No account, no plugin, no upload. Three steps and your model is on screen.
Drop in your file
Drag the .gcode onto the viewer, or click to browse. If the model references separate material or texture files, drop the whole folder or a .zip so everything resolves.
Inspect the scene
Orbit, pan and zoom to look around. The inspector lists every mesh in the hierarchy with its triangle count, and reports the bounding box so you can sanity-check scale.
Convert or capture
Save a PNG of the viewport, or download the model converted to GLB, OBJ, STL, PLY or USDZ — all without the file leaving your browser.
What is a G-code file?
G-code is not a 3D model. It is the instruction language for machine tools — a sequential list of movements, temperatures and speeds — standardised as far back as RS-274 in the 1960s for CNC machining, and adopted by 3D printers through the RepRap project.
A .gcode file is what a slicer produces from your model. Where an STL describes a shape, G-code describes the exact path a nozzle will travel to build it: G0 for rapid moves, G1 for controlled moves with extrusion, plus commands for temperature, fan speed and retraction, layer by layer.
That difference matters. By the time a model becomes G-code, every decision is already baked in — layer height, infill density, wall count, supports, orientation and print speed. The file is specific to one machine configuration and cannot be meaningfully edited back into a shape.
Visualising the toolpath is genuinely useful before starting a long print. Seeing the actual extrusion paths reveals problems a model preview cannot: missing supports, gaps where walls failed to join, travel moves crossing open space that will string, or a first layer that does not sit properly on the bed.
This viewer draws the movement paths as lines, distinguishing extrusion from travel. It is a geometric preview, not a simulator — it does not estimate print time, filament use or collisions, which your slicer already reports.
G-code at a glance
- Extension
- .gcode
- Origin
- RS-274, 1960s CNC
- Encoding
- Plain text commands
- Produced by
- Cura, PrusaSlicer, Bambu Studio
- Describes
- Toolpaths, not geometry
- Key commands
- G0 travel, G1 extrude
- Machine specific
- Yes
What this viewer supports
- G0 and G1 movement paths rendered as lines
- Extrusion distinguished from travel moves
- Output from all common slicers
- Layer-by-layer path structure
- Print time and filament estimates
- Converting G-code back to a solid model
- CNC milling G-code with arcs (G2/G3)
G-code viewer FAQs
The questions we get asked most about opening G-code files.
Is my G-code uploaded anywhere?
No. The file is parsed and drawn entirely in your browser. Nothing is sent to A23D or stored.
Can I convert G-code back into an STL?
No, and no tool can do it properly. G-code describes the path a nozzle travels, not the shape it produces — the model was discarded at slicing time. You would need the original file, or to remodel it.
Why does my G-code look like lines rather than a solid?
Because that is what it is. G-code is a movement path, so the viewer draws the actual travel of the print head. Seeing the paths is the point — it shows what the printer will physically do.
Will this estimate my print time or filament use?
No. This is a geometric preview of the toolpath. Your slicer already calculates time and filament from its own machine profile, and its figures will be far more accurate.
Does CNC milling G-code work?
Partially. Linear moves render, but arc commands G2 and G3 — common in milling and rare in FDM printing — are not interpreted, so those sections will be missing or misdrawn.
Which slicers are supported?
Output from all the common ones renders, including Cura, PrusaSlicer, Bambu Studio, Simplify3D and Slic3r, since they all emit standard G0 and G1 movement commands.
More format viewers
All browser-based, all free, nothing uploaded.
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