3D Print Toolbox checks a mesh for the problems a slicer will choke on, and reports them before you export. It replaces the round trip most people do instead: export an STL, push it through a repair tool or the slicer, read the error list, come back and guess which faces it meant. Here the checks run in the sidebar and results are selectable in edit mode, so you jump straight to the geometry at fault.
What It Does
- Checks for non-manifold and bad contiguous edges, self-intersections, degenerate faces and edges, non-planar faces, thin geometry, sharp edges and overhangs — individually or all at once
- Counts mesh islands with a Shells check
- Attempts repair with a single Make Manifold operator
- Calculates volume and surface area, which is how you cost a print in advance
- Hollows a solid to a consistent wall thickness without self-intersections
- Rotates a model flat to the bed from a selected face, and scales to a target volume or bounding box
- Exports the selection to STL, PLY or OBJ, skipping the file dialog once an absolute path is set
Good To Know
- Free and open source under GPL-3.0-or-later, maintained by Mikhail Rachinskiy, originally written by Campbell Barton
- Version 1.4.1, Blender 4.2 LTS and newer, 146 KB; 612,000+ downloads, rated 5.0 from 51 reviews
- It reports far more than it fixes. Make Manifold is the only repair operator. Thickness, overhang, intersections and non-planar faces are diagnostics with no fix button — those you solve by remodelling
- Make Manifold handles small defects; on badly broken meshes or scan data it produces unpredictable results. Keep a copy before running it
- Apply object scale before analysing. A non-unit scale has been shown to produce spurious intersection warnings
- Overhang and non-planar counts are almost never zero on a curved model. Both flag ordinary geometry by design, and the docs concede quads are rarely flat
- The 4.2 minimum oversells it. Shells needs 4.3+, the Bisect tool needs 4.5+, and the modifier-based Hollow needs 5.0+
- The exporters disagree about modifiers: STL follows viewport settings, PLY follows render settings. A modifier visible in one but not the other lands in only one file
- No 3MF export — the maintainer treats exporters as out of scope and points to a separate extension
Where It Fits
If you model for FDM or resin in Blender, this saves a round trip on every print, and the volume readout alone justifies the install. It is a validator, not a repair suite — the slicer stays the authority on overhangs and thin walls, and badly damaged meshes still need a proper remesher.