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Analyze and repair STL files online

Check the mesh before 3D printing: find holes, non-manifold edges, flipped normals and degenerate triangles, verify dimensions and minimum wall thickness, and repair detected errors directly in the browser.

You can also reduce triangle count, compare the model with common build volumes and download the corrected STL file. Geometry is processed locally and is not uploaded to CastaliaLab servers.

Topology analysis · Mesh repair · Wall thickness check · Simplification · Download corrected file

Your model stays on your device.

Workspace

Upload, analyze and repair your STL

Drop an STL into the panel · mouse: orbit · wheel: zoom · right-click: pan.

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Check an STL file before printing

An STL file can look fine in a viewer and still contain errors that break slicing or printing. Surface gaps, non-manifold edges, inconsistent normals and degenerate triangles can cause missing walls, unexpected infill or volumes interpreted incorrectly.

The tool analyzes geometry and topology, highlights detected issues and lets you review them before production.

If the model comes from a scan or conversion, you may also want to read about our 3D scanning service and file preparation workflow.

Topology analysis and mesh repair

Analysis finds errors that prevent the mesh from describing a closed volume correctly. The report separates holes, open edges, non-manifold connections, flipped normals, degenerate triangles and separate components.

When geometry allows, repair rebuilds missing areas and fixes detected inconsistencies. You can verify the result in the viewer and download a new STL file.

Holes and open edges

An open edge means the surface is interrupted. When open edges form one or more loops, the model does not bound a volume correctly and may be interpreted wrongly by slicing software.

Non-manifold edges

A mesh is non-manifold when connections cannot uniquely represent a solid surface — for example, an edge shared by too many faces or parts linked ambiguously.

Flipped normals

Normals indicate which side of a face points outward. When some are flipped, software may confuse inside and outside of the model.

Degenerate triangles

Faces with zero or near-zero area, often from coincident or nearly aligned vertices. Even when invisible, they can break later operations.

Minimum wall thickness analysis

A topologically clean mesh is not necessarily printable. Walls that are too thin may not build, may break when removing supports or may deform in use.

The thickness map highlights areas below your threshold so you can quickly spot walls, details and fillets that may be critical. The threshold can be tuned to your process and material.

What the thickness map shows

The visualization marks zones where the distance between opposite surfaces is below the selected value. It checks locally thin areas, not just outer dimensions.

Correct thickness depends on the process

There is no single minimum wall valid for every print. A wall that works in FDM 3D printing may behave differently in resin, MJF or metal printing. Orientation, material, wall height, load and finish also matter.

Technical note: thickness analysis is a preliminary geometric check. It does not replace structural verification or a full manufacturing review.

Repair that follows surrounding geometry

Closing a hole with a flat patch can work on some shapes but looks wrong on curved, organic or irregular surfaces.

Adaptive repair reads the opening contour, nearby face orientation and triangulation density. When enough surrounding shape remains, the missing zone is rebuilt to follow the surface more faithfully.

If a large portion of the model is missing, the system may rebuild a coherent surface without knowing the original shape with certainty. Always verify the result before printing.

Reduce STL file weight

More triangles do not always mean more precision. Beyond the resolution you actually need, the file becomes heavier and harder to process without a real printing benefit.

Simplification reduces triangle count and lets you monitor deviation from the original geometry. Reduction can be strong on flat surfaces; on small details and curved areas, proceed gradually.

Before export, see also our guides on preparing an STL file for 3D printing.

Check dimensions and build volume

The tool reads model dimensions and lets you change scale. You can compare the part envelope with common build volumes to see whether the model fits the selected machine when oriented inside it.

The comparison uses geometric envelope only. Supports, safety margins, orientation and material shrinkage must be assessed separately. FDM: 250×250×250 mm. Resin: 353×196×350 mm. MJF: 380×284×380 mm. Metal: 140×140×140 mm. Larger parts can be split and reassembled.

Local processing in the browser

Analysis, visualization and geometry operations run directly in your browser. STL geometry is not uploaded to CastaliaLab servers.

How to analyze and repair an STL file

  1. 1
    Upload the file

    Select the STL from your computer or drag it into the upload area.

  2. 2
    Review the report

    Check topology errors, model dimensions and any areas below the thickness threshold.

  3. 3
    Apply corrections

    Repair the mesh, change scale or reduce triangle count depending on the result you need.

  4. 4
    Verify and download

    Visually check the modified model and download the new STL before opening it in your slicer.

Frequently asked questions

Does the tool check wall thickness too?
Yes. The thickness map highlights areas below the selected threshold and helps spot walls and details that may be too thin to print.
Does thickness checking guarantee the part is printable?
No. It is a preliminary geometric check. Printability also depends on process, material, orientation, supports, tolerances and part function.
Can the tool repair any STL file?
It can fix many topological errors but cannot reconstruct extended missing regions with certainty when not enough geometry remains. Complex cases may need manual work.
What does non-manifold STL mean?
The mesh has connections that do not uniquely describe a solid surface — for example edges shared by too many faces or surfaces linked ambiguously.
Is the file uploaded to your servers?
Geometry is processed locally in the browser and is not uploaded to CastaliaLab servers.
Can I reduce triangle count?
Yes. Simplification lightens the file and lets you monitor deviation from the original geometry.
Does repair change dimensions?
Topological repair should not change overall model size. Rebuilt zones may differ from the original shape when information is insufficient.
What is the maximum file size?
The tool accepts files up to 100 MB. Whether processing completes also depends on triangle count, mesh complexity, browser and available memory.
Which errors are detected?
The report can find holes, open edges, non-manifold edges, inconsistent normals, degenerate triangles and other mesh issues.
Is the tool free?
Yes. Analysis, repair and download can be used without registration.
Can I open the result in Bambu Studio, Cura or PrusaSlicer?
Yes. The exported STL opens in common slicers including Bambu Studio, Cura, PrusaSlicer and OrcaSlicer.

Guides on preparing files for 3D printing

Prepare an STL file

Format, scale, resolution and checks before printing.

Read the guide

Repair a damaged mesh

How to recognize holes, non-manifold edges and inconsistent normals.

Read the guide

Choose minimum wall thickness

How walls and details change across FDM, resin, MJF and metal.

Read the guide

© Castalia S.r.l. — All rights reserved on code, copy and the “Castalia Lab” brand. Use of this tool is subject to the terms of use (no reverse engineering, scraping, redistribution, or use to train competing products, to the extent permitted by law).

Professional help

Does the file need manual reconstruction?

If the model has missing parts, severely damaged surfaces or geometry that must be rebuilt accurately, we can review the case and work on the file manually.

Request a file review Explore 3D modeling