Model doctor

A model that renders fine can still be broken

That is the whole problem with importing someone else’s 3D file, and it is the reason this page exists. The preview looks right, so you assume the file is right, and you find out otherwise three steps later — when the rig explodes on the first frame of animation, when the model imports into Unity at 100× the size of everything else, when a bake comes back as noise because two triangles were sharing the same patch of texture.

None of that is visible in a render. All of it is visible in the data.

What it checks

Scale — models authored in centimetres arrive 100× too big, and models exported from a sculpt can arrive so small they vanish. Fixable, and fixed.

Bind pose — if a skinned mesh’s inverse bind matrices are not invertible, the rig detonates the moment it is posed. Fixable: the skeleton is rebound to its current pose.

Normals — faces wound the wrong way make a model look inside-out from one side. Fixed when the mesh is unambiguously inverted, and reported but left alone when it is not (see below).

UVs — overlapping islands mean you cannot bake anything into the texture. Reported, never silently "fixed": the map has to be rebuilt, which is a different operation with different trade-offs.

Topology and holes — non-manifold edges, degenerate faces, open boundary loops. Reported; the repair tool is where you act on them.

Why it refuses to fix some of what it finds

The inverted-normal test asks whether each face points away from the centre of its mesh. That is a sound question for a convex, closed, single object, and a misleading one for anything else — a croissant sitting on a baking tray, modelled as one mesh, honestly reads as half inside-out. So the doctor only flips a mesh that is overwhelmingly inverted, and for the ambiguous cases it tells you what it saw and leaves your model alone.

This is deliberate. A tool with no viewport and no undo button should be the conservative one. An automatic fix that is right nine times out of ten is a tool that quietly ruins one model in ten.

How to use it

1. Drop your .glb, .gltf or .fbx into the box above.
2. Leave "fix what can be fixed safely" on unless you only want the report.
3. Press Diagnose. Every check reports what it found, and what — if anything — was done about it.
4. Download the corrected GLB. If nothing needed changing, you get no file, and it says so.

Questions

It found problems but produced no file. Why?

Because some problems cannot be fixed in place — overlapping UVs need the map rebuilt, holes and non-manifold edges need geometry removed. The doctor reports those and points you at the tool that acts on them, rather than pretending a re-export was a repair.

My model imports into Unity 100× too big. Will this fix it?

Yes — that is the classic centimetres-versus-metres mismatch, and the scale check catches and corrects it.

It says my normals "lean inward" but did not flip them.

The test compares each face against the mesh centre, which is only reliable on a convex, closed shape. A concave or multi-part mesh trips it legitimately, so on an ambiguous result the doctor reports and stops. Open it in the editor if you want to flip them while watching the result.

Is anything uploaded?

No. Every check runs on your machine, in this tab.

The other tools

• Reduce polygons — Cut the triangle count of a GLB, GLTF or FBX and keep the textures. Runs in your browser.
• Compress GLB — Resize and re-encode the textures, and cut the triangle count if the mesh is the problem. In your browser.
• Repair a 3D model — Weld split vertices, drop degenerate faces and stray islands, fill holes, flip inverted normals.
• Everything else Rig Bake does — rigging, retargeting, spritesheets, VFX.