How to Open and View G-code Files

A sliced G-code file is the set of instructions your printer will receive. Opening it in a viewer is a useful final check when a file came from another computer, was sliced with an unfamiliar profile or simply needs a quick visual review before printing.

Use the G-code Viewer and Preflight Checker to open a .gcode, .gco or .gc file locally in your browser. It reads the file only: it does not upload, execute, send or modify it.

Open the file and inspect its parsed layers

Choose the sliced file from your device. The viewer reads common linear motion commands, groups recognised paths by layer and presents a 2D preview.

1. select a G-code file from your device;
2. check that the summary reports readable layers and motion;
3. use the layer selector, scrubber or previous and next buttons to move through the preview;
4. compare solid extrusion paths with the optional dashed travel paths;
5. read the per-layer move count and the parser limitations before making a print decision.

The preview is most useful for catching an obviously unexpected shape, missing looking paths, a surprising Z range or movement that extends beyond the area you expected.

What to inspect in a G-code viewer

A viewer can provide practical file-level context without making assumptions about a particular printer. Review the information the file actually contains:

• parsed layer count and Z range;
• extrusion and travel paths on representative early, middle and final layers;
• parsed X, Y and Z motion extents;
• slicer comments, declared print time and filament details when present;
• hotend and bed targets that the parser recognises;
• coordinate modes, extrusion mode, tool markers and limitation warnings.

For a more detailed final checklist, use the guide to checking G-code before printing.

Why a browser preview differs from slicer simulation

A slicer knows the model, its configured printer profile and feature-specific decisions it made while generating the file. A browser viewer instead reads a conservative subset of the finished text file. It can accurately display the paths it recognises, but it does not run firmware or recreate the complete slicer environment.

Treat the preview as an independent inspection aid, not a replacement for the slicer's native preview. Confirm the selected printer, material, orientation, supports and start sequence in the slicer that produced the file.

Read limitations before relying on the preview

G-code dialects vary between slicers, firmware and printer workflows. Arcs, macros, conditional logic, vendor-specific commands and multi-tool workflows may be incomplete or absent from a general parser's preview. A limitation notice does not necessarily mean the file is wrong; it means the viewer cannot make a reliable claim about that part of it.

When a limitation matters to your workflow, return to the slicer's native preview and confirm the file against the intended printer and firmware.

Use G-code viewing after model preflight

G-code viewing is the final file-level stage. Before slicing, use STL Print Preflight or 3MF Print Preflight to inspect the model itself. Then check dimensions, geometry, wall thickness and overhang risk as relevant, slice with the intended printer profile, and view the resulting G-code before printing.

No browser inspection can guarantee print success. Firmware configuration, machine condition, material, calibration, bed preparation and physical environment remain part of the real print outcome.