STL, OBJ & 3MF check and repair

Check your STL for errors: holes, non-manifold edges, flipped normals and wrong units

Upload a mesh and get a report that names each problem, the file it is in and how many edges or triangles it affects. If you want, you also get a cleaned copy as a new STL. Your original file is never changed.

START HEREUpload your modelSTL, OBJ, 3MF

Upload STL / OBJ / 3MF See an example report

What it changes and what it only reports

Fixes automatically

Optional. You tick the box and confirm first.

Removes duplicate triangles
Removes zero-area triangles
Flips a closed mesh that is inside out

Saved as a new STL. Your upload stays as it is.

Only reports

You fix these in your modelling software.

Holes and open edges (not watertight)
Non-manifold edges
Normals that disagree between neighbouring faces
Self-intersecting triangles
Walls thinner than your minimum (sampled)
Loose vertices and a missing unit

FREE3 jobs a dayFiles up to 10 MB · up to 100,000 triangles

PROUp to 200 jobs a day€12.99/month or €89.99/year

See plans

No account needed for free jobs. Models up to 500,000 triangles need Pro. Failed jobs are never counted.

No account for free jobs
Original file never overwritten
Results deleted after 24 hours

EXAMPLE REPORTSample data

housing.stl238,442 triangles · unit mm, confirmed

ErrorHoles: 4 open boundary loops182 open edges. Reported, not filled.
WarningThin wall0.62 mm sampled, below your 0.80 mm minimum
RepairCleaned STL availableDuplicate and zero-area triangles removed. Holes left as they are.

What you downloadHTML report, mesh preview image, metrics CSV, the optional repaired STL and a manifest that lists every file

Formats, limits & file handling

Works with: STL, OBJ, 3MF with one object
Free job: Up to 3 files · 10 MB each · 100,000 triangles
Largest job (Pro): 10 files · 128 MB total · 500,000 triangles per model
You receive: HTML report, mesh preview, metrics CSV, optional repaired STL and manifest
File handling: Unfinished drafts deleted after 2 hours · encrypted results after 24 hours

THREE STEPS

From your STL to a list of what to fix.

01
Upload and pick the unit
STL and OBJ files carry no unit, so you choose mm, cm or in. Set the minimum wall thickness (0.8 by default).
02
Decide on the cleaned copy
Tick the repair box and confirm what it may change, or leave it off to get the report only.
03
Download the report
Findings per file with counts, a mesh preview, a metrics CSV and the optional STL. Failed jobs are never counted.

Example report

See a report before you upload a real file.

This example uses made-up data in the same layout as a real report.

✓

Nothing is uploadedExample only

housing.stl

The mesh needs work before slicing

You confirm the unit first. 3MF files with several objects, components or transforms are rejected instead of being measured wrongly. A clean report does not guarantee a successful print.

What this check covers: mesh topology and sampled geometry. It does not simulate a slicer or printer.

ErrorHoles: 4 open boundary loopshousing.stl · 182 open edges · not filled
WarningThin wall0.62 mm sampled, below the 0.80 mm minimum
RepairCleaned STL availableDuplicate and zero-area triangles only; holes are never filled

Triangles: 238,442
Open boundaries: 4
Unit: mm · confirmed

Show the download contents

HTML report, mesh preview, metrics CSV, optional repaired STL and a manifest with a hash for every file.

What the check looks at

Every finding comes with the file name and a count

Holes and open edges.Edges used by only one triangle mean the mesh is not watertight. They are grouped into loops, so you can see how many holes there are.
Non-manifold edges.Edges shared by more than two triangles.
Normals.Neighbouring faces wound in opposite directions, and closed meshes that are inside out (negative volume).
Self-intersections.Triangles that cut through each other. The scan tests a set number of triangle pairs and says so when it reaches that limit.
Thin walls.Sampled distances compared with the minimum you set. This is a sample, not a full wall-thickness map.
Small defects.Duplicate triangles, zero-area triangles and vertices that belong to no face.
Size.Model dimensions in the unit you confirmed.

What it does not do

It does not fill holes, fix self-intersections, flip single faces or simulate a slicer, printer or material. Printability is never guaranteed.

Clear answers

STL check & repair FAQ

Which mesh files can I check?

STL, OBJ and 3MF files that contain a single object. Free jobs take up to 3 files of up to 10 MB and up to 100,000 triangles. Larger jobs with up to 10 files, 128 MB and 500,000 triangles per model need Pro. 3MF files with several objects, components or transforms are rejected instead of being measured wrongly.

Does it fill holes in my STL?

No. Holes, open edges, non-manifold edges and self-intersections are reported with the file name and a count, but they are not closed or rebuilt. Fix them in your modelling software, then check the file again.

What does the repair step actually change?

Only three things, and only after you tick the repair box and confirm the scope: it removes duplicate triangles, removes zero-area triangles and flips a closed mesh that is inside out. The result is a new STL file. Your uploaded file is never overwritten.

Why do I have to confirm the unit?

STL and OBJ files carry no unit, so the same file can be read as millimetres, centimetres or inches. You pick the unit before any size or wall-thickness figure is produced.

Does a clean report mean the print will succeed?

No. Wall thickness is sampled rather than measured everywhere, and nothing here simulates a slicer, a material or a printer. Printability is never guaranteed.

Available now

Check your STL before a long print.

3 free jobs a day with no account, or up to 200 a day with Pro. Holes are reported, not filled.

Upload STL / OBJ / 3MF See the example report