Repair an STL file online
Open the model your slicer warns you about. It is repaired on this device - the file is never uploaded - and you turn it around in 3D before you save the repaired copy.
Drop an STL file hereOpen an STL file
STL, OBJ or 3MF. It is read on this device and never uploaded.
A large model takes a few seconds.
What it repairs
- Holes Gaps in the surface are closed with a patch.
- Flipped triangles Faces pointing into the model are turned out.
- Pinched edges Surfaces that only touch are parted by a micron.
- Duplicate triangles Copies are removed, and walls of no thickness cancel out.
Repair
A resin or powder printer traps liquid resin or loose powder in them: add drain holes, or fill them. A filament printer prints them as they are.
Still open
These need a modelling tool such as Blender or Meshmixer.
Self-intersections
Finds surfaces that cut through each other and paints them yellow. A slicer usually joins parts that overlap; a surface cutting through itself it may not. Nothing is changed.
Printer
Material
Overhangs
Thin walls
Paints red every wall thinner than {limit} mm. The file is {height} mm tall: type the height you print it at.
Click the model to read the wall there.
* An estimate, not a guarantee. The repair and the checks read only the file’s shape - not your printer, filament or slicer settings - and can be wrong either way: what is marked here may print well, and what looks clean may still fail. Your slicer has the final word: preview the sliced model before you print.
When the slicer warns about the model
Bambu Studio says it in red under the object’s name - “Error: 1 non-manifold edge”, and often “reversed faces detected, which may affect rendering” - and sends you to a third-party tool to repair it. PrusaSlicer and OrcaSlicer mark the object with a warning sign and count its open or non-manifold edges. This is that tool, and it takes three steps:
- Open the STL above, or drop it onto the box. It stays on your device.
- Read the result and turn the model around: the list says what was repaired, and anything still open.
- Save the repaired STL and load it into the slicer in place of the original.
Bambu Studio and OrcaSlicer on a Mac or Linux
Their Fix model command uses a repair built into Windows, so on a Mac or Linux it is not there and the warning stays. Repair the file here, on any system, and load the repaired copy in its place.
The original file is never changed: the repaired copy is saved beside it under its own name, ending in -repaired.
What the repair does
Holes
A gap in the surface - a missing triangle, a face the exporter dropped - leaves the slicer guessing where the inside is. Each hole whose rim is one clean loop is closed with a flat patch facing the same way as the surface around it. A sheet that encloses nothing even once closed, like a single flat panel, is left as it is.
Flipped triangles
Every triangle says which side is outside by the order of its corners. One turned the wrong way shows as a dark patch in the slicer and can make it fill the wrong side. Triangles are turned to match their neighbours, then each separate part is turned outward, and the cavity inside a hollow part inward.
Pinched edges and points
Where two surfaces only touch - two parts meeting along an edge, a fold that closes on itself, two cones tip to tip - three or more triangles share one edge and the slicer reports it as non-manifold. The surfaces are parted: the shared corner is copied and each copy moved a micron into its own surface. Nothing a printer can resolve changes.
Duplicate and empty triangles
A triangle written twice is kept once. Two copies facing opposite ways are a wall of no thickness, usually the face two touching parts share, and both are removed so the parts become one solid. Triangles whose corners merged into a line or a point cover nothing and are dropped, and so is a loose scrap - a few triangles hanging apart from the model, far smaller than it and enclosing nothing.
What it checks
Beside the repair, each on request: whether the model fits your printer, about what it weighs and the filament or resin it takes, where it overhangs past the angle a slicer supports, where its walls are too thin for your nozzle and where its surfaces cut through each other - each painted on the model, each an estimate from its shape.
What it does not repair
Surfaces that cut through each other, walls too thin to print, and a missing side of a model too big to call a hole are not something a repair can decide for you: they need a modelling tool. The result says when any of these is left.
Questions people ask
Is my file uploaded?
No. The page loads the repair into your browser, and the model is read, repaired and saved on your own device. Nothing about it is sent to us or to anybody else - once the page has loaded, it works with the network switched off.
Why does my slicer say the model is non-manifold?
Because some edge of it is not shared by exactly two triangles: either one triangle (a hole) or three and more (surfaces that only touch). Bambu Studio, PrusaSlicer and OrcaSlicer all check for this, and most models downloaded from the web have a few such edges.
Does the repair change the shape of my model?
Only where it repairs. A closed hole gets a flat patch, a parted point moves by a thousandth of a millimetre, and everything else is written back exactly as it was. The 3D view shows the repaired copy before you save it.
How large a file can it open?
As large as the device has memory for. A computer handles models of several million triangles; a phone gives up sooner, and then says so rather than saving half a model.
Does it open 3MF or OBJ files?
Yes: it opens STL (binary or ASCII), OBJ and 3MF, a 3MF in its own unit with every placed object, and saves the repaired model as STL or 3MF. A Bambu Studio or OrcaSlicer project of one object on one plate is saved back as that project, with its plate, settings and paint.
Is it free?
Yes, with no sign-up and no limit on how many files you repair.
How accurate are the checks?
They are an estimate from the model’s shape alone, and can be wrong either way. A wall painted thin, an overhang or an edge left open may slice and print well, and a model that looks clean here may still fail: the slicer knows your nozzle, layer height, supports and material, and this page does not. Always preview the sliced model before printing. The tool is free and provided as is, without any warranty: we are not responsible for prints, material or time lost on a file repaired or checked here.
Keep every model with its print figures
LayerFlow3D keeps your models with what the slicer measured - grams, hours, plates - and prices every order from them.