STL topology check

STL Manifold Checker: Open and Over-Shared Edges

Check how STL triangles join: exposed edges, edges shared by too many faces and vertex-connected pieces. The result helps locate a topology question; it cannot infer the intended solid or detect every spatial intersection.

Check your STL topology

Choosing and submitting a file uploads it for server analysis. The guest limit is 25 MiB. Download the public controls below without uploading your own model.

Choose STL file

Select a non-empty .stl file, up to 25 MiB.

What this check reports

Finding	Meaning
One triangle at an edge	Boundary or open edge; design intent remains unknown.
Two triangles at an edge	Ordinary shared edge; winding is checked separately.
Three or more triangles at an edge	Over-shared edge, labelled “non-manifold edge” in the report.
Component count	Groups connected by any exact shared vertex in this server report, not defect count. Local repair selection uses complete shared edges instead.

The 10-face open cube reports four boundary edges. The 13-face duplicate cube reports three over-shared edges. Two intended closed cubes report two components with no edge defect.

Try an example

Question to explore

Does this STL have an exposed edge, an over-shared edge, or two intentional closed pieces?

Settings: Load a public control locally. Press Check manifold geometry only if you want to submit it for a server report; selecting the file alone does not submit it.

Example file

Downloads this public control, then opens it locally. Your own file can still be chosen above.

Read the explanation · Download and compare controls · Methods and processing

If your report says...

Finding	Narrow next action
Boundary edges	Inspect the opening with the hole guide before filling anything.
Over-shared edges	Use the focused topology repair workflow to determine the intended face.
Multiple vertex-connected components	Review the separate-shell guide before keeping or removing any piece.

Method and limits: the server compares exact stored vertex positions, excludes degenerate triangles from edge counts, and connects components through shared vertices. It does not run a complete vertex-manifold or spatial-intersection test. A malformed STL returns an error, not a clean zero. For exposed-boundary interpretation alone, use the STL Watertight Checker.