G-code Tools

The slicer (FDM) gives you G-code; sometimes you need to inspect, edit, or programmatically modify it before printing. Visualizers, post-processing scripts, and Klipper macro libraries cover this gap.

G-code visualizers (browser)

• ★ gcode.ws / GCode Analyzer — free; drop a .gcode file in the browser, get layer-by-layer playback, time and filament estimates. The "what does this print look like?" go-to.
• ★ Kiri:Moto's preview — full G-code preview alongside its slicer/CAM view; runs locally.
• NC Viewer (ncviewer.com) — browser; CNC-leaning but reads FDM G-code fine.
• OctoPrint G-code viewer plugin — preview within OctoPrint.
• Mainsail / Fluidd live preview — built-in G-code rendering for queued + active prints.

G-code visualizers (desktop / library)

• Repetier-Host G-code preview — bundled with Repetier-Host; mature, cross-platform.
• gcodeviewer (npm) — embeddable in your own web app; powers some hosted tools.
• OrcaSlicer / PrusaSlicer / Bambu Studio preview — built-in; the most accurate (knows about retraction, MVS, AMS swaps).

Post-processing scripts

• ★ PrusaSlicer / OrcaSlicer Post-processing scripts — point at any executable; runs after every slice. Standard hook for purge-tower tweaks, M73 progress injection, etc.
• ★ Klipper macros (gcode_macro) — defined in printer.cfg; run on the host, can call any Python or shell. The most flexible runtime hook.
• Cura PostProcessingPlugin scripts — Python scripts that run inside Cura.
• gcode-preprocessor, community Python scripts on GitHub — pause-at-layer, color-change at layer, M600 swap, ironing tweaks.

G-code macros & community libraries

• ★ Klipper-Macros (th33xitus/klipper-macros) — the canonical START_PRINT / END_PRINT / PAUSE / RESUME / CANCEL macro library for Klipper.
• ★ PrusaSlicer / OrcaSlicer macro snippets — community-maintained start/end G-code templates per printer.
• NevermoreMacros — bed-fan / chamber-fan automation for enclosed printers.
• Mainsail / Fluidd macro UI — both UIs let you wire macros to one-tap buttons.

Pause-at-layer / color change / multi-color tooling

• ★ OrcaSlicer "Add pause at layer" / "Change filament at layer" — built-in; emits proper M600 / M601 / pause sequences.
• PrusaSlicer custom G-code at layer — same idea, slightly less polished UI.
• HueForge — paid (cheap); generates filament-change G-code for full-color filament prints (lithophanes + multi-color flat art). Companion to MakerWorld and Printables image-to-print workflows.
• Fullcontrol.xyz — free; programmatic G-code generation in Python; useful for vase-mode art and experiments.

G-code editors / inspectors

• Notepad++ / VS Code with .gcode syntax — surprisingly common; G-code is just text.
• OctoPrint Terminal tab — send raw G-code commands during a print.
• Mainsail / Fluidd console — same.
• gcode_lint — community linters that flag suspicious moves before printing.

Time & filament estimation

• ★ OrcaSlicer / PrusaSlicer / Bambu Studio built-ins — accurate enough; calibrated to the slicer's speeds.
• gcode.ws — second-opinion estimate.
• klipper_estimator — open-source CLI that re-estimates G-code time based on Klipper's actual motion config (input shaping, accel limits). Often more accurate than the slicer estimate on a tuned Klipper printer.
• OctoPrint PrintTimeGenius plugin — adaptive time estimation.

Conversion / arc-fitting / optimization

• ★ arc-welder — open source; converts G1 line segments to G2/G3 arcs for smaller files and smoother motion. Available as OctoPrint plugin and CLI; built into Klipper as gcode_arcs.
• G-code optimizer (community) — deduplicates consecutive moves, useful for vase mode.
• OrcaSlicer "Arc fitting" — built-in setting; emits G2/G3 directly.

Programmatic G-code (write your own)

• ★ Fullcontrol — Python lib for generating G-code from scratch (great for non-planar, vase-mode, calibration-experiment art).
• gcodepy / mecode — Python G-code emitters.
• Vase-mode generators (community OpenSCAD scripts) — single-perimeter spiral G-code from a contour.

Pick this if…

• Quick "what's this G-code do" check: drop it into gcode.ws.
• Custom start/end behavior on every print: Klipper macros (Klipper) or post-processing scripts (slicer-side).
• Multi-color or pause-at-layer: OrcaSlicer's built-in tools, plus HueForge for full-color art.
• More accurate time estimates than the slicer gives: klipper_estimator.
• Smaller G-code, smoother arcs: arc-welder or your slicer's arc-fitting toggle.
• Generate G-code programmatically: Fullcontrol.