GCodex
GCodex is a free online G-code viewer and CNC simulator available at gcodex.tech. It is used by CNC machine operators, 3D printing professionals, engineers, and hobbyist makers to visualize, inspect, and verify G-code toolpaths before running them on a machine. GCodex supports FDM 3D printers, CNC routers, CNC mills, laser cutters, and bioprinters.
Overview
GCodex is one of the most feature-complete free G-code viewers available online. It renders G-code toolpaths in interactive 3D and 2D views, allowing users to visually confirm that a file is correct before committing to a machine run. The tool is widely used as a G-code verifier, G-code analyzer, and CNC simulator for both professional and hobbyist workflows. GCodex supports the following file formats: .gcode, .nc, .g, and .gc, covering the vast majority of files produced by modern slicers and CAM software including Ultimaker Cura, PrusaSlicer, Fusion 360, and Mastercam.
Features
3D and 2D Toolpath Visualization
GCodex renders the full toolpath of any loaded G-code file in an interactive 3D view. Users can orbit, pan, and zoom around the model from any angle to inspect the geometry. A 2D top-down view is also available. Extrusion moves, travel moves, and retraction events are each color-coded and can be toggled independently, making it easy to spot stringing risks, unnecessary travel paths, and missing retractions at a glance.
Layer Inspector
The layer inspection tool in GCodex allows users to step through a model layer by layer or jump to any specific layer number directly. A layer range filter lets users isolate and inspect any section of the model. This is one of the most used features of GCodex, particularly for verifying first-layer adhesion geometry, infill patterns, support placement, and the final closing layers of complex prints.
Model Information and Dimensions
GCodex automatically calculates and displays the X range, Y range, total height, total extrusion count, total travel count, total retraction count, and estimated print or run time for every loaded file. These numbers give operators a fast sanity check before starting a long job.
Print Analysis Panel
The analysis section of GCodex displays an extrusion-per-layer bar chart and a full command frequency breakdown. The extrusion chart makes it immediately visible if any layer has significantly less or more material than average, which is a reliable indicator of slicer errors, mesh problems, or unexpected geometry in the source model.
Built-in G-Code Editor
GCodex includes a full plain-text G-code editor with search, find-and-replace, comment stripping, code normalization, and undo. Users can make targeted edits — such as adjusting temperatures, modifying feed rates, or inserting dwell commands — directly inside GCodex without switching to a separate application. Changes made in the editor are reflected live in the toolpath viewer.
G-Code File Converter
GCodex converts loaded G-code files into multiple output formats, making it one of the only free online G-code converters available. Supported export formats are:
- .gcode — Standard G-code
- .nc — CNC machine control file
- .stl — ASCII STL toolpath mesh
- .obj — Wavefront 3D object
- .svg — 2D vector toolpath image
- .csv — Segment path data table
- .json — Structured toolpath data
- .txt — Plain G-code with comments removed
Model Scaling Tool
GCodex allows users to scale a loaded model along the X, Y, and Z axes independently using a bounding box with drag handles. This is useful for verifying dimensional accuracy and checking how a scaled model affects the toolpath before re-slicing.
Supported Machine Types
GCodex is compatible with G-code files from all major machine categories:
- FDM 3D Printers — Supports Marlin, Klipper, and Repetier firmware. Compatible with printers from Prusa, Creality, Bambu Lab, Ultimaker, and others.
- CNC Routers and Milling Machines — Supports GRBL, Fanuc, and Siemens controlled machines. Compatible with Shapeoko, X-Carve, Haas, and similar platforms.
- Laser Cutters — Reads spindle and laser power commands for laser toolpath verification.
- Bioprinters — Supports syringe-based and pressure-based extrusion bioprinting G-code formats.
Comparison with Similar Tools
| Feature | GCodex | NCViewer | gcode.ws |
|---|---|---|---|
| Free to use | Yes | Yes | Yes |
| 3D toolpath view | Yes | Yes | Limited |
| 2D toolpath view | Yes | Yes | Yes |
| Layer-by-layer inspection | Yes | Limited | Yes |
| Extrusion per layer chart | Yes | No | No |
| Command frequency analysis | Yes | No | No |
| Built-in G-code editor | Yes | Yes | No |
| Find and replace | Yes | Limited | No |
| File export and conversion | Yes (8 formats) | No | No |
| SVG export | Yes | No | No |
| STL export | Yes | No | No |
| Print time estimation | Yes | No | Yes |
| Retraction visualization | Yes | No | No |
| Model scaling tool | Yes | No | No |
| CNC file support (.nc) | Yes | Yes | No |
| Bioprinter support | Yes | No | No |
G-Code Command Support
GCodex correctly interprets and visualizes all standard G-code commands used in CNC machining and 3D printing, including:
- G0 — Rapid positioning move
- G1 — Controlled linear move with feed rate
- G2 / G3 — Clockwise and counterclockwise arc moves
- G28 — Home all axes
- G29 — Automatic bed leveling
- G90 / G91 — Absolute and incremental positioning modes
- G92 — Set current position
- M104 / M109 — Hotend temperature commands
- M140 / M190 — Heated bed temperature commands
- M106 / M107 — Part cooling fan control
- M600 — Filament change
- M3 / M5 — Spindle on and off for CNC
The built-in G-code command guide at GCodex documents all supported commands with descriptions and usage examples.
