THE FREE MESH WORKBENCH
Free STL viewer
& mesh checker.
Check an STL online before moving into CAD. Rotate your mesh, confirm its dimensions, and review triangle count and available edge diagnostics.
Binary or ASCII · up to 100 MiB / 500,000 triangles
Your file stays in your browser. This tool never uploads it.
Try a mesh with a known result.
Compare a closed cube, missing face, reversed triangle and shared-edge example. Each test file includes its expected dimensions and diagnostic counts.
Download the free STL test files →START WITH A KNOWN MEASUREMENT
How to check an STL online
Choose your STL
Open a binary or ASCII .stl file, or try the sample bracket. The viewer reads the file on your device; your model is never uploaded.
Confirm units and size
Select the units used when the model was exported and compare its bounding dimensions with a known measurement. Selecting units changes the interpretation, not the file.
Understand STL units and scale →Review the findings
Rotate the preview, read the triangle and edge results, then download the JSON report or project brief. Use the findings to choose a repair, conversion, or rebuild workflow.
Understand boundary and non-manifold edges →What the tool checks
Triangle count, bounding dimensions, surface area, and zero-area triangles use the full parsed model. For meshes with up to 25,000 triangles, it also counts boundary edges, non-manifold edges, and inconsistent edge orientations. The preview may sample up to 20,000 faces to stay responsive.
STL does not reliably identify physical units. Choose the intended units and compare a known measurement. An edge check is a useful diagnostic; it does not detect every geometry defect or certify printability.
What to do next
For a one-off cut, try a CAD conversion and check the result. For repeated changes to hole diameters, wall thickness, or mounting positions, a new model built around those dimensions may be more useful.
STL to STEP in FreeCAD or Fusion →Change an STL hole diameter or spacing →
Resolve FreeCAD’s “shape is not a shell” error →
Prepare a STEP handoff for a machine shop →
Find why walls disappear after slicing →
Explore STL-to-CAD rebuilds →
BEFORE YOU CONVERT
STL checker questions
Understand what the inspection tells you before treating the results as a repair plan.
Is this STL viewer free, and is my file uploaded?
The checker is free and requires no account. STL parsing, the 3D preview, and report downloads happen in your browser. Your model is not sent to MeshRebuild. The separate inquiry form sends the information you type; it does not attach your STL.
Which files and sizes can I inspect?
The tool reads binary and ASCII STL files with an .stl extension, up to 100 MiB and 500,000 triangles. STEP, OBJ, and 3MF are not supported. If your STL exceeds the limits, preserve the original and export a lighter copy from your mesh editor.
Can I measure STL dimensions in millimeters or inches?
The report gives the axis-aligned bounding box in your selected model units. Choose millimeters, centimeters, meters, or inches to match the source export. STL has no reliable stored unit, so confirm the interpretation against a known physical measurement. Bounding dimensions depend on the orientation of the part.
Check a scale mismatch →What does “edge check skipped” mean?
Edge diagnostics are limited to meshes with 25,000 triangles or fewer to keep the browser responsive. Larger supported files still receive the full triangle count, bounding dimensions, surface area, and zero-area triangle count. A skipped check is not a clean result; inspect the mesh separately in a mesh editor before conversion.
Open the mesh repair checklist →Does a closed edge result prove the STL is printable?
No. It means the checked edges connect consistently using exactly matching vertex coordinates. This tool does not test self-intersections, wall thickness, clearances, or manufacturing requirements. Review the model in the software used for your intended process.
Can this tool repair an STL or convert STL to STEP?
The tool inspects and previews STL; it does not repair geometry or export STEP. Follow the conversion guide for FreeCAD or Fusion. If the converted body does not support the changes you need, consider a mechanical CAD rebuild with an agreed scope.
Read the STL-to-STEP workflow →