Best Free & Open-Source G-code Editors & Simulators Software

Before a CNC machine cuts the first chip, every command must be right. G-code errors can waste materials, damage tools, or crash spindles — making verification and simulation critical steps in the programming workflow.

Fortunately, several free and open-source G-code editors and simulators allow machinists, CAM programmers, and educators to preview, optimize, and debug toolpaths before running them on real equipment. These tools bridge the gap between CAD/CAM output and the machine, ensuring accuracy and safety without adding license costs.

1. Camotics

Best for: 3D G-code simulation and toolpath visualization.
Camotics is the most popular open-source G-code simulator for milling and routing. It simulates material removal in 3D, displays feed rates, and calculates machining time. It supports multiple tool definitions and works offline.
License: GPL / Open Source.
Used by: Machine shops, educators, and CNC programmers for verification before machining.

2. NC Viewer

Best for: Quick online G-code preview and validation.
NC Viewer runs directly in a browser, requiring no installation. It supports standard milling and turning paths, displays coordinates and feed speeds, and includes syntax highlighting for editing.
License: Free / Web-based.
Used by: CNC programmers needing a fast online G-code check.

3. OpenCNCPilot

Best for: G-code inspection and optimization for GRBL-based machines.
OpenCNCPilot combines visualization with basic editing, Z-compensation, and height-map generation. It’s particularly suited for desktop mills, PCB routers, and hobby machines.
License: GPL / Open Source.
Used by: DIY machinists and small workshops.

4. GCodeSimulator + Editor (Android)

Best for: Mobile G-code preview and syntax inspection.
This Android app simulates G-code line-by-line, offering 2D and 3D visualization and feed/time estimates. Ideal for quick review on the shop floor.
License: Freemium / Mobile.
Used by: CNC operators and students checking programs on the go.

5. NCPlot (Free Edition)

Best for: G-code backplotting and macro variable analysis.
NCPlot offers a limited free version that supports text editing, backplotting, and G-code macro inspection (Fanuc-style). Paid versions add advanced simulation, but the free tier remains strong for basic verification.
License: Freemium / Proprietary.
Used by: Job shops using Fanuc or Haas CNCs.

6. G-Simple

Best for: G-code creation and basic simulation for 2.5D milling.
G-Simple is a free Windows CAM and G-code tool that includes basic geometry creation, drilling, and pocketing. It also previews toolpaths before exporting G-code.
License: Freeware.
Used by: Hobby machinists and educational programs.

7. bCNC

Best for: GRBL control and G-code manipulation.
bCNC is both a machine controller and editor for GRBL-based CNCs. It provides visualization, auto-leveling, toolpath optimization, and direct machine control.
License: GPL / Open Source.
Used by: Makerspaces and small CNC router operators.

8. Universal Gcode Sender (UGS)

Best for: Sending, editing, and visualizing CNC jobs.
UGS is an open-source GRBL controller with built-in G-code viewer, syntax highlighter, and feed control. Ideal for running CNC jobs and testing G-code edits live.
License: GPL / Open Source.
Used by: CNC router users and educators.

9. NC Corrector

Best for: 3D G-code simulation with editing tools.
NC Corrector supports lathe and milling toolpaths, highlighting errors, tool movements, and collisions. It’s a strong offline option for training and NC validation.
License: Freeware.
Used by: Educational labs and machining instructors.

10. G-Code Q’n’Dirty

Best for: Fast lightweight editing.
This minimalistic editor reads large NC files quickly, supports syntax coloring, and includes line-number tracking for debugging. No simulation, but perfect for text-based editing.
License: Freeware / Open Source.
Used by: Experienced programmers editing directly in G-code.

G-code Software Comparison Table

G-Code Editor Recommendations

For complete 3D simulation, Camotics remains the open-source standard.
For web-based verification, NC Viewer and OpenCNCPilot deliver instant feedback without heavy installs.
If you prefer GRBL-based systems, bCNC and UGS combine editing with real machine control.
For education and training, NC Corrector provides a great environment for teaching G-code structure and motion visualization.

In 2025, machinists no longer need to trust their toolpaths blindly. Free and open-source G-code simulators now offer real-time visualization, verification, and optimization once exclusive to commercial CAM suites. Whether you run a 3-axis router, a precision mill, or a school CNC lab, these tools help you see the code before it cuts — reducing crashes, scrap, and uncertainty while giving full control back to the programmer.

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