G-code Viewer Online
LocalFree G-code viewer online: open .gcode/.nc/.tap and preview CNC toolpaths in 3D — timeline replay, simulation and safety checks. No upload, no sign-up.
Drag files here, or click to browse
Supports GCODE, NC, GCO, TAP, CNC, NGC
Choose fileG-code is rendered locally in your browser; nothing is uploaded. Lengths are shown in mm; inch (G20) programs are converted to mm (1 in = 25.4 mm). Large programs are parsed synchronously on the main thread — the page may be briefly unresponsive while parsing (cannot be cancelled mid-parse).
What is it? G-code Viewer displays and 3D-previews G-code toolpaths in the browser: timeline playback along the path (play/pause, 0.5–8× speed), a 2.5D material-removal simulation in three views (depth-shaded, colored by last cutting tool, or stepped cumulatively by Z depth layer), static safety checks (missing F words, negative feed, rapids below the deepest cut, missing tool/end/units words), per-tool color legend, bidirectional source↔toolpath seeking and tool stats. Supports .nc/.gcode/.tap/.gco/.cnc/.ngc files; rendering uses the open-source gcode-preview library (MIT).
TL;DR: G-code Viewer previews CNC and 3D-printing toolpaths in 3D, right in your browser. Drop a .nc or .gcode file — it renders automatically — and inspect the highlighted source, timeline playback, 2.5D material-removal simulation and static safety checks. Free with no sign-in; rendered locally, nothing is uploaded.
How to use
- Drop a .gcode / .nc / .tap file — the toolpath renders in 3D automatically (or click Load sample).
- Drag the progress slider to step through moves, click a source line to seek, or press Play for a timeline replay (0.5–8× speed; dragging pauses it, it stops at the end and replays from the start).
- Inspect the 2.5D material-removal simulation (depth-shaded, by last cutting tool, or stepped by Z depth layer — cumulative top-down coverage) and the tool legend/stats (view only, no output file).
- Read the Safety checks card: missing F words, negative feed, rapids below the deepest cut, missing tool/end/units words — click a line number to seek the toolpath there (static checks only).
FAQ
Is it local?
Yes — the toolpath is parsed and rendered in your browser.
Which G-code flavors work?
Standard G0/G1/G2/G3 motion is supported; vendor-specific macros are ignored.
Does playback change anything?
No — playback only previews tool motion along the path; the final preview and any exports are unaffected.
Can it check my G-code before machining?
Partly. The Safety checks card statically scans for missing F words, negative feed rates, rapids below the deepest cut, and missing tool/end/units words — each finding links to its line in the toolpath. Tool compensation, macros and machine travel limits are not validated.
Which file types can I open?
.gcode, .nc, .tap, .gco, .cnc and .ngc are all accepted as long as the content is standard G-code; G0–G3 motion is parsed and vendor-specific macros are ignored.
Does it work for 3D-printing G-code?
Yes — extrusion and travel moves render the same way, and per-tool coloring and Z-depth layer steps work for printer programs.
Is it really free?
Yes — viewing, replay, simulation and safety checks are free with no sign-in. The tool runs entirely in your browser, so nothing is uploaded.
What is a G-code file?
G-code is the programming language of CNC machines and 3D printers (RS-274 lineage): a plain-text list of commands telling the controller where to move, how fast, and which tool to use. Programs are saved as .gcode, .nc, .tap or similar extensions, and they describe tool motion rather than geometry, which is why viewing them is the quickest way to verify a finished program.
Examples
- Drop a .nc / .gcode file → 3D toolpath preview
- Click a source line to seek the toolpath · press Play for a 0.5–8× timeline replay
- Open a .tap or .cnc file → read safety-check findings and click through to the toolpath
Supported formats
Limitations
- Very large programs are parsed in full and may exhaust browser memory — the whole file is rendered, nothing is downsampled. Parsing runs synchronously on the main thread: the page may be briefly unresponsive while parsing and cannot be cancelled mid-parse.
- View only; no G-code is generated or modified, and playback is a motion preview only.
- Numeric readouts (stats, 2.5D simulation) are in mm — inch (G20) programs are converted at 1 in = 25.4 mm; the 3D canvas renders in the program's original units.
- Arcs are measured by their true arc length (full circles = 2πR); tool compensation and macros are not parsed.
- The simulation canvas is a fixed-resolution raster approximation; tool colors repeat every 8 tools (the legend says so when it applies). The by-layer view is a cumulative top-down projection of cuts down to the selected depth, not a cross-section.
- Safety checks are static scans only — tool compensation, macros and machine travel limits are not validated.
- Runs locally in your browser, files are never uploaded.
Privacy
Privacy first: this tool runs entirely in your browser — your input and files never leave your device, and everything is cleared when you close the page.