Free STL repair, in your browser

Drop in an STL, 3MF or OBJ. Ten checks run on your own machine, you watch each one resolve, and you get the repaired file — plus the part every other repair tool leaves out: what it deliberately would not guess at, and why.

• Your file never leaves the tab
• No queue, no timeout
• STL, 3MF and OBJ
• Every check named, passed or failed

What it repairs

The defects with one correct answer. Every one of these is reported by name and count when it is applied, measured on the geometry actually written out rather than asserted from what was attempted.

• Welds split vertices. The commonest STL defect: a surface torn in the file but identical in space.
• Removes zero-area triangles. Including three distinct corners on a straight line, which index checks miss.
• Removes duplicate faces. The same face wound the same way, twice.
• Corrects face winding. What Bambu Studio calls reversed faces, propagated across the surface.
• Turns an inside-out surface right side out. A mesh that is consistent and wholly inverted still encloses a negative volume.
• Caps small flat holes. Each gap closed from its own rim — which is what makes the volume, and every cost from it, real.

What your slicer is telling you

The error a slicer shows is rarely the name of the defect. These are the same ten checks this tool runs, phrased the way the problem usually arrives.

Bambu Studio says “reversed faces detected”. What does that mean?

Some triangles are wound the opposite way round from their neighbours, so the slicer cannot tell which side is the inside of the part. It is one of the defects with a single correct answer, so this repairs it: the winding is made consistent across the surface, and if the whole mesh turns out to be inside out it is turned right side out as well.

My slicer says the model is not watertight, or not manifold. Can you fix it?

Sometimes, and the tool tells you which. Small flat holes are capped from their own rim. A hole whose rim is concave or twisted is left open and named instead — the patch we could build would close the surface with overlapping triangles that are not the surface the designer drew, and an open hole you can see beats a bad cap you cannot. Non-manifold edges, where three or more faces meet along one line, are reported and never guessed at.

Why does my model show the wrong volume or weight?

Three causes, and the audit distinguishes them. The surface may be inside out, so it encloses a negative volume. It may be open, in which case there is no well-defined inside at all. Or it may hold separate shells that disagree about which side is solid, whose signed volumes cancel — which produces a confident, meaningless figure. In that last case the number is withheld rather than shown, because a wrong volume becomes a wrong filament cost and a wrong price.

The file imports as several separate objects. Is that a defect?

Not necessarily — plenty of models are genuinely several parts. The tool counts the shells and tells you how many there are. It does not merge them: if they are meant to be one solid, that needs a boolean union, which is real computational geometry rather than something to approximate on a mesh somebody is about to print.

What is a self-intersection, and do you repair it?

It is a surface that passes through itself. The scan searches for them and reports how many pairs of triangles it found; it never repairs them. Resolving one means re-cutting and re-stitching geometry. On a very large model the search can run out of budget, and when it does the tool says the defect is neither ruled out nor fixed rather than reporting the file as clean.

Is my file uploaded anywhere?

No model file or filename is uploaded. Repair runs inside this tab. When usage reporting is enabled, opening the tool records a random visit ID and referral/campaign information. Scanning records a geometry fingerprint, format, byte size and diagnostic counts even without a repair. Repair events add geometry measurements, actions and print-readiness settings; download requests and any print outcomes or notes you submit are also recorded. This metadata is stored in Supabase and readable only by authorized FilamentIQ administrators. See the usage-data disclosure beside the file picker for the current reporting status. Local repair works even if reporting is unavailable.

Which file formats does it accept?

STL in both binary and ASCII, 3MF, and OBJ. A 3MF project exported straight from Bambu Studio, Orca or PrusaSlicer works as-is. The repaired file can come back out as 3MF, binary STL or ASCII STL.

Is there a file size limit, or a queue?

There is no queue, because the work runs on your machine rather than on a shared server — so there is no timeout either, and a large model takes as long as your laptop takes. The one hard limit is 1,500,000 triangles, enforced while the file is being read so an oversized model is refused rather than allocated and then rejected.