What is a G-Code viewer?

A G-Code viewer is a tool that visualizes CNC machine and 3D printer toolpaths from G-code files. It lets you inspect layer-by-layer movements, extrusion paths, travel moves, and verify your file before running it on a machine. GCode provides a free online G-Code viewer that runs entirely in your browser — no upload required.

How do I view a G-code file online for free?

With GCode, you can view any G-code file online for free in seconds. Simply drag and drop your .gcode, .nc, or .gc file onto the viewer, or click 'Open File' to select it. The tool processes the file locally in your browser — nothing is uploaded to any server. You get a full 3D and 2D toolpath visualization instantly.

Can I simulate G-code without uploading it?

Yes. GCode simulates G-code files entirely in your browser. Your file is never uploaded to any server. All processing — parsing, rendering, simulation — happens locally using WebGL and JavaScript. This makes it faster and more private than cloud-based alternatives.

What G-code formats does GCode support?

GCode supports all standard G-code formats: .gcode, .gc, .nc, .g files. It works with G-code generated by Marlin, Klipper, RepRap, GRBL, Smoothieware, and most CNC and 3D printer firmware. It supports G0/G1 moves, G2/G3 arcs, M-commands, and absolute/relative positioning.

How is GCode different from NCViewer?

GCode offers more features than NCViewer: it includes layer filtering, detailed print analysis (extrusion count, travel moves, retracts, estimated time), syntax-highlighted G-code view, multiple export formats (STL, OBJ, SVG, CSV, JSON), and visibility toggles for extrusion, travel and retract moves. Both tools are browser-based and free.

Can I analyze G-code layers separately?

Yes. GCode has a Layer Filter control that lets you set a minimum and maximum layer range. You can isolate any single layer or a range of layers to inspect the toolpath in both 3D and 2D views. The current layer is displayed in real time on the 3D viewport.

What is the best free online G-code viewer?

GCode is one of the most feature-rich free online G-code viewers available. It offers 3D and 2D toolpath visualization, layer analysis, extrusion/travel/retract highlighting, G-code syntax highlighting, print time estimation, and export to multiple formats — all running locally in your browser with no upload or signup required.

How do I verify my G-code before running on a CNC machine?

Load your G-code file into GCode and use the 3D viewer to visually verify the toolpath. Check for unexpected movements, inspect individual layers using the Layer Filter, toggle travel moves on/off to see only cutting/extrusion paths, and review the Analysis tab for move counts and distance metrics. This helps catch errors before running on expensive CNC machines.

GCodex — Free Online G-Code Viewer, Simulator & Analyzer

Drag sliders to scale model

Edit

Read-only — click to edit Edit Mode

Print Analysis

Detailed G-code inspection & metrics

Extrusion per Layer

Command Frequency

File Converter

Export your loaded G-code as another format — all processing happens in your browser

Select Output Format

G-Code

Standard CNC / 3D printer

.gcode

NC File

CNC machine control code

.nc

STL

Toolpath mesh — ASCII STL

.stl

OBJ

Wavefront 3D mesh object

.obj

SVG

2D vector toolpath top view

.svg

CSV

Path data table per segment

.csv

JSON

Structured path data (API-ready)

.json

Plain Text

Raw G-code, comments stripped

.txt

G-Code: Exports your file as-is. Use for re-download or sharing with a machine.

STL / STEP / OBJ → G-Code

Converting 3D model files (STL, STEP, OBJ) to G-code requires a slicer — a separate application that handles mesh analysis, support generation, and toolpath calculation. This is computationally intensive and cannot run reliably in a browser.

Recommended Slicers (Free)

Ultimaker Cura Best for FDM — supports STL, OBJ, 3MF, STEP ↗ Open PrusaSlicer Advanced profiles, supports bioprinting setups ↗ Open CuraEngine CLI Command-line slicing — integrate in your pipeline ↗ Open

No file loaded

Drop a .gcode or .nc file, or click "Open File" to start visualizing

Layer — / —

click to inspect

Extrusion

Travel

Retract

Seg 0 / 0

Speed