3D slicing software like Bambu Studio, OrcaSlicer, PrusaSlicer, and Cura requires solid, manifold boundary representation (B-Rep) to compute internal toolpaths. When a 3D model contains unclosed surfaces, inverted normals, or missing polygons, slicers cannot distinguish inside from outside, leading to slicing errors and hollow voids. This tool parses binary and ASCII STL files in browser memory, highlights open boundary edges, and closes planar holes to produce watertight meshes.

### Topological Mesh Diagnostics & Repair The tool evaluates 3D triangle vertex connectivity using topological half-edge data structures: - **Edge Shared Count**: Evaluates every triangle edge. In a watertight manifold solid, every single edge must be shared by exactly two adjacent faces. - **Naked Boundary Detection**: Identifies open boundary edges (edges belonging to only one triangle), highlighting unclosed holes in isometric wireframe previews. - **Planar Hole Triangulation**: Collects contiguous loops of naked edges and constructs fan triangulation caps that seal open planar voids. - **Watertight Verification**: Re-evaluates edge topology post-repair to confirm zero remaining boundary edges before writing a clean binary STL output.

### Worked Mesh Repair Example Upload an unstitched scan or broken CAD export (`scan_bracket.stl`): - **Initial Diagnostics**: 42,180 triangles, 36 open boundary edges (Status: Non-Manifold / Unclosed). - **Repair Algorithm**: Traces the 36 open edges into two circular boundary loops, generating 34 new triangulated cap faces. - **Post-Repair Status**: 42,214 triangles, 0 open boundary edges (Status: Watertight 100% Manifold). - **Download**: Exports a repaired binary `.stl` file ready for error-free 3D print slicing.

### Private In-Browser Geometry Processing All STL byte buffer parsing, floating-point vertex mapping, and binary mesh exports run strictly on your local machine using client-side JavaScript. No 3D models or proprietary CAD files are uploaded to remote servers.