Fix Your Broken STL — and See Exactly What Was Wrong

Drop in an STL that won't slice. Get back a watertight file plus a plain-English report: how many holes were filled, how many faces were flipped, what got cleaned up. Everything runs inside your browser.

Drop your STL file here

or

Nothing is uploaded — the repair runs on your own machine.

What It Fixes

These are the four errors behind most failed slices. The repair pipeline handles all of them in one pass, then tells you which ones it actually found in your file.

Holes and open edgesA surface with gaps isn't a solid, so the slicer has nothing to fill. Boundary loops are detected and closed, and you're told how many holes were filled.
Non-manifold geometryEdges shared by three or more faces, and bowtie vertices, make the topology ambiguous. These are separated and rebuilt into clean, printable geometry.
Flipped normalsWhen some faces point inward, the slicer can't tell inside from outside and prints hollow shells or nothing at all. Every face is re-oriented outward.
Degenerate and duplicate facesZero-area triangles, duplicate faces and stray vertices confuse slicers and inflate file size. They're removed, and the count is reported back to you.

See how the repair works, step by step

You Get a Report, Not Just a File

Most online repair tools are a black box: you drop a file in, watch a spinner, and get something back with no idea what changed — or whether it worked. This one shows the actual repair log. Holes filled. Faces flipped. Vertices welded. Zero-area triangles removed. Whether the result is watertight, how many separate shells it contains, and an honest note when a check was skipped because the model was too large.

Read what each diagnostic means

About This Tool

STL Repair runs entirely inside your browser. Your model is never uploaded, never stored, and never leaves your computer — you can disconnect from the internet after the page loads and it still works. There's no signup, no account, and no file limit beyond what your own machine can handle.

The repair engine is built on open-source geometry libraries used in production by Blender, Godot and OpenSCAD. Before repairing, the tool reads your file's triangle count and tells you roughly how long it will take — so you know upfront whether it's a two-second job or a thirty-second one, instead of staring at a spinner.

Frequently Asked Questions

Is my STL file uploaded to a server?

No. The repair engine is compiled to WebAssembly and runs on your own machine. Your file is read locally by the browser and never transmitted. You can verify this yourself: load the page, disconnect from the internet, and the tool still repairs files normally.

How large a file can it handle?

It depends on your machine, so the tool tells you before you commit. A 5 MB model (about 100,000 triangles) takes roughly 4 seconds on a desktop. A 24 MB model (500,000 triangles) takes around 26 seconds on a desktop and over a minute on a phone. Above roughly 50 MB you're better off with a desktop application.

What does 'watertight' actually mean?

A watertight mesh has no gaps: every edge is shared by exactly two faces, so the surface fully encloses a volume. Slicers need this to tell inside from outside. If a model isn't watertight, the slicer either refuses it or produces hollow, broken toolpaths.

Will repairing change how my model looks?

Undamaged areas are left alone. The pipeline only modifies what it needs to — filling holes, re-orienting faces, removing degenerate triangles. A model that is already clean comes back with its geometry unchanged. Filled holes are flat patches across the gap, so a large missing region will look bridged rather than reconstructed.

Is it really free?

Yes. No signup, no account, no watermark, no usage limit. The site is supported by advertising.