STL Validator

What this validator checks

Each rule below is validated independently and reported with an exact count — never a single pass/fail score. An STL file is valid (watertight) only when every rule passes: zero boundary edges, zero non-manifold edges, zero winding conflicts, zero duplicate faces, and a completed self-intersection scan that finds none.

• Manifold validation — every edge must be shared by exactly two triangles.
• Boundary validation — open edges are grouped into closed loops, open chains, branches or non-simple shapes.
• Winding validation — adjacent triangles must agree on traversal direction across a shared edge.
• Duplicate-face validation — no triangle may exactly repeat another's three vertices.
• Orientation validation — closed, consistently-wound shells are checked for inward (inverted) orientation via signed volume.
• Self-intersection validation — no two triangles may geometrically cross, outside expected shared-edge adjacency.
• Degenerate-triangle detection — zero- and near-zero-area triangles are found and excluded from every rule above.

Validation error reference

"Has boundary edges" / open mesh error

Real gaps in the surface exist — the closed-loop count usually corresponds to the number of holes.

"Has non-manifold edges"

At least one edge is shared by three or more triangles — an ambiguous, non-manifold surface at that edge.

"Has winding conflicts"

Two adjacent triangles disagree on winding direction, even though the edge itself is manifold.

"Has duplicate faces"

At least one triangle exactly repeats another's three vertices, same or reversed winding.

"Self-intersections found"

At least one pair of triangles genuinely overlaps in 3D space.

"Self-intersections not checked"

The model was too complex to fully validate within this tool's safety limits — reported honestly, never as a pass.

How validation results are computed

Validation starts from exact-identity vertex matching (bit-exact float32 comparison, never a distance tolerance — a tolerance would change the model's real topology and could mask a genuine gap). From there, an edge-incidence table classifies every edge, boundary edges are grouped into components, triangles are grouped into connected shells, each shell's orientation is propagated and its signed volume computed when meaningful, duplicate faces are grouped by canonical vertex identity, and self-intersections are found via a spatial-grid broad phase plus a robust triangle-triangle test.

Validation limitations

• This tool validates only — it never modifies, repairs or re-exports a file.
• A passing validation result does not certify printability; a failing one does not mean a file can't be sliced.
• Every check has a disclosed safety limit; a check that can't finish safely is reported as skipped, never as passed.

After validation: repairing errors

This validator identifies problems only. STL Repair — a planned, separate MeshWrench tool — will fix what's found here (holes, inverted normals, non-manifold geometry) locally in your browser, once it ships.