Pilot, You Are Cleared for Launch.
preFlight is an advanced 3D printing slicer. What began as a fork of PrusaSlicer has quickly grown into something completely unique. Slic3r, the legacy 15+ year-old code at its core, has been retired and replaced by Luminary, our ground-up reimagining of the engine. The UI layer is now DSKY and the entire dependency stack underneath has been modernized. preFlight natively imports PrusaSlicer, SuperSlicer and now OrcaSlicer profile bundles, so you can be up and running in minutes. To put it mildly, this is no ordinary fork.
Flagship Engineering
Athena Perimeter Generator
Something familiar, but completely different. Fixed extrusion widths with independent overlap control. Negative values create gaps for flexible materials.
Interlocking Perimeters
10-15% estimated Z-strength increase. Oversized beads compress into the interlocking pattern on the layer below. Fundamentally different from "brick layers."
Modern Stack
Luminary, preFlight's own slicing engine, replaces the fifteen-year-old libslic3r. True 64-bit architecture, C++20, Clipper2, and a fully modernized dependency stack. Roughly 50% less RAM usage.
Sidebar (Re)Slicing
Open the Sidebar inside the Preview and every change reslices in place, without a trip back to Prepare or a second press of Slice Platter. Prepare never slices on its own.
Overrides
Every setting an object, part or modifier can carry, in one panel with a checkbox per row. Unchecked rows show the live project value, so you can see what you are changing from.
Performance
Slicing on Windows is 10 to 17% faster and reslices rerun only the steps a change affects. A 31 million segment Preview went from 170 to 670 ms per frame down to 27 to 98 ms.
Full Lighting and Supersampling
Shadows, ambient occlusion and physically based shading in Prepare and Preview. Toolpaths cast and receive shadows. Supersampling up to 2x, applied without a restart.
G-code Preprocessing
Embedded Python scripting with 130+ APIs. Per-move access to feedrate, flow, acceleration, junction angle, and region geometry. Bundled Python 3.14 runtime.
Export to Script
Hand your G-code to a Python script at export. Save to disk, upload via FTPS, send to any networked printer, or all three at once. No proprietary API, just standard Python.
OrcaSlicer Import
PrusaSlicer profiles import natively. OrcaSlicer profiles go through a 230+ setting mapping engine with value transforms, G-code macro translation, and inheritance resolution.
Baobab Supports
New support engine that lives somewhere between Organic and Snug. Baobab grows thick trunks that expand into a canopy matching the shape of the support interface.
Serpentine
Every island of a layer printed as one continuous line that snakes back and forth through the wall thickness, in place of separate perimeters and infill. Radial strength and short anchored overhangs.
Nip & Tuck Seams
V-shaped channel that absorbs start/stop blobs. Painted seam alignment with bidirectional blending and 0.1mm brush precision.
2-opt Travel Optimization
Nearest-neighbor ordering refined by 2-opt segment swapping, applied to infill region by region. Travel distance drops 30 to 50% on multi-island layers.
Maximum Commands Per Second
Diagnose printer stuttering at high speeds. See exactly how many G-code segments per second your settings generate per feature type.
Preview Clipping Plane
See inside your sliced objects with a cross-sectional clipping view. Right-click any object in the Preview to clip.
Paint-on Multi-Type Supports
Paint different support types (Snug, Grid, Organic, Baobab) on different areas of the same object: Baobab under a large overhang, Organic under a surface you want to keep clean.
Counterbore Bridge Gizmo
Per-hole bridge layer control with smart fill. Fill direction adapts to each hole's corridor angle independently for optimal bridging.
CMYK+W Color Mixing
Multi-filament color blending using Beer-Lambert transmission physics. Paint any achievable color directly onto your model with up to 512 palette entries.
Align to Face Gizmo
Precisely position objects against any face of another model. Click a face, place an object, and combine with boolean operations for clean results.
Relief Gizmo
Turn an image into a 3D heightmap object with thickness, smoothing and gamma controls, then seat it on a model with Align to Face and weld or subtract it.
Mission Critical
Easy Switching
Natively imports PrusaSlicer and SuperSlicer profiles. OrcaSlicer bundle import translates 230+ settings, converts values, and maps G-code macros, then lists every setting it dropped and every value it had to collapse.
Every Platform
Windows x64 and native ARM64. macOS on Apple Silicon and Intel, signed and notarized. Linux via AppImage. Raspberry Pi 5 via .deb. One codebase, so every platform gets every feature.
Works With Any Printer
Compatible with any modern 3D printer running RepRap-flavored G-code. STL, OBJ, 3MF, AMF, and STEP file support.
Free and Open Source
Licensed under GNU AGPL v3. We could have made this only valuable to our own customers. We didn't. This is us giving back to a community we've been part of for over 10 years.
Security First
All Windows binaries digitally signed. macOS notarized by Apple. 3MF post-process scripts suppressed on import. In-memory extraction prevents Zip Slip.
Active Development
We use preFlight daily and ship improvements constantly. The commit history, issue tracker, and changelog speak for themselves.
Your Workspace, Your Way
40+ themes, from the default dark to Catppuccin, Nord, Dracula, Gruvbox and Solarized. Accordion or tabbed layouts, an Edit Visibility mode that hides any setting you never touch, and categories that collapse and stay the way you left them. Pinned preset selectors with print settings, printer, nozzle diameter and filament controls. With multiple extruders, one numbered selector strip instead of a section per extruder.
Physics-Based Time Estimation
Print time predictions that model the firmware's own motion planning. Klipper limits (max velocity, acceleration, square corner velocity, minimum cruise ratio) match the fields in printer.cfg, and SET_VELOCITY_LIMIT mid-print is honored. For RepRapFirmware, limits are retrieved directly from your connected printer. Real-world compensation lets you dial in the algorithm to your specific machine.
Tuned for Your Hardware
Cap slicing threads and prefer P-cores on Intel hybrid processors. Full lighting with shadows and ambient occlusion, supersampling up to 2x, and a Smooth layer lines filter for the Preview, applied without a restart. Mouse navigation schemes matching Blender, Fusion 360, SolidWorks and Tinkercad. Includes a fix for NVIDIA's threaded optimization conflict.
Ready to Strap In? You Have a Go for Download.
Free and open source under the GNU AGPL v3. A modern C++20 foundation with Luminary, preFlight's own slicing engine.