Tiny Online Tools
Two questions, two tests
"Does this need supports?" is really two separate questions, and this tool answers both because a model can easily pass one and fail the other.
The facet-angle test is the one your slicer uses. Every triangle in the mesh is measured against the build plate: 0° is a flat down-facing surface, 90° is a vertical wall. Anything shallower than your support threshold gets counted, weighted by surface area rather than by triangle count, and broken into bands so you can see whether the geometry sits just past the limit or hangs fully horizontal. This is cheap and it matches the number in your slicer profile — but it is blind to context. It cannot tell a shallow chamfer that the layer below holds up from a ledge hanging over nothing.
The per-layer island test slices the model at your layer height and compares each layer with the one beneath it. Material printed over nothing is unsupported area. Within that, one case is far worse than the rest: a region of a layer with no overlap at all with the layer below is a floating island — the nozzle would be extruding into mid-air. Those are flagged as severe, because they fail outright rather than merely printing badly.
Reading the results
The 3D view colours every facet by its angle: red where the surface is flat and unprintable, amber at your threshold, cool blue where it is steep enough to be safe, grey for anything facing up. The chart below it shows unsupported area layer by layer, so the problem layer is one click away; the cross-section then draws that layer over the one beneath it with the overhanging part in red.
About the material estimate
The support volume is a rough estimate, not a simulation. It projects each unsupported region down to the plate, removes the part itself, and scales the result by a density factor. A real slicer adds interface layers, XY expansion, tree branches and a base — expect its number to differ. Use this to compare orientations, not to buy filament.
STL and OBJ carry no units, so tell the tool what one unit in the file means. Everything runs in your browser; the model never leaves your machine.