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Your slicer will not flag a bad STL

You print STL files that customers, designers or download sites send you. Some of them are broken in ways you cannot see: two solids touching along a line, or a gap in the surface. The slicer slices them anyway, and what prints at the bad spot is a guess. Send us the files. We count every edge and tell you which ones are wrong, with the exact spot.

Check your STL

Why the slicer does not catch it

The slicer slices it anyway. It turns the surface into layers as best it can. On our tray it gave a time and a weight and no warning.

Every edge has two faces. In a closed solid each edge is shared by exactly two triangles. One face means a hole. Three or more means solids touching along a line.

Touching is not joined. Two parts that meet only along an edge may print fused, cracked or apart. The file does not say which.

60 files, one broken edge

We ran fabkit's mesh check over 60 STL files from our own CAD work on 15 October 2026. 59 were closed solids. One was not:

  • 59brackets, wheels, pins, frames, casesevery edge shared by exactly 2 faces
  • 1a 90 x 114 x 30.5 mm board tray, 300 triangles1 edge on 4 faces: a 21.5 mm vertical line at X40.0 Y51.9 where a tab meets the wall. No hole.
  • A1the same tray in BambuStudio 2.08 on an A1sliced with no warning: 1 h 17 min, 34.9 g of PLA

Try one of yours. It is counted in your browser and never leaves your computer:

Pick an STL to count its edges.

This counts edges only. Our full check also measures volume, wall thickness and fit on your printer.

What you get

Every edge counted
Open edges and edges on three or more faces, with the coordinates of each, so you can find it in your CAD.
Volume and size
The real volume of a closed part, its size, and whether it fits your printer.
Thin walls
The thinnest wall measured inside the part, and where it is.
A plain verdict
PASS, FAIL or CANNOT DETERMINE for each file, before it reaches a printer.

Check your STLs

Tell us what you print. We answer within one working day.

We answer within one working day.

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