Focused STL tools
How to edit an STL file in four steps
- Drop the model on the viewer above or press Open File. Any format the viewer reads opens here.
- Press Edit. The Edit model panel slides in on the right with its sections: Size; Rotate, mirror, move; Cut with a plane; Combine & booleans; Reduce triangles; Repair; Add text.
- Open a section, set the numbers and press Apply. Every Apply is one step, and Undo / Redo at the top of the panel walks back through the last 20.
- Press Convert and pick STL or 3MF to download the edited part.
The file on your disk is never touched. Only the download carries the changes.
Rotate, mirror, move and lay on bed
A downloaded model often arrives lying on its side or far from the origin. Under Rotate, mirror, move you turn the part about X, Y or Z by any angle; the field starts at 90° about Z. A part exported from a Y-up program usually needs 90° about X.
Mirror X/Y/Z makes the left-hand version of a bracket. The normals stay outward after the flip, so your slicer still sees a solid and not an inside-out shell.
Move shifts the part by the X, Y and Z values you type. Lay on bed drops the lowest point to Z = 0, and Center on origin puts the middle of the part at 0, 0.
Combine two models with booleans
In Combine & booleans, press Add another file and choose whether the new model lands next to the first one or at the same center. The added model becomes part B and everything already open is part A.
| Button | Result | Typical use |
|---|---|---|
| A ∪ B | one body made of both | glue a base or a handle onto a model |
| A − B | A with the shape of B removed | a pocket, a slot or a socket for a magnet |
| A ∩ B | only the volume both share | keep the part of a model inside a box |
| Union all parts | every separate shell merged | a file with loose pieces that should print as one |
The boolean engine is manifold-3d, and it wants closed meshes. If A or B has holes, the tool asks you to run Repair first. The STL repair page explains the check and the fix.
Add raised or engraved text
Add text writes up to 40 characters on the top of the part in Noto Sans Bold, Latin or Cyrillic. Set the letter height and depth in millimetres, then choose Raised on top or Engraved into top. The panel starts at 8 mm letters, 1 mm deep.
A part number or a name on a keychain takes one Apply. Text needs a watertight base, like the booleans.
What this STL editor does not do, and where to go
The tool changes the whole mesh with exact numbers. Four kinds of jobs need another program:
- Sculpting and dragging single vertices: use a sculpting app.
- Hollowing with a set wall thickness: your slicer's wall and infill settings, or a resin slicer.
- Smoothing or remeshing a rough scan: a mesh tool built for scans.
- Supports: add them in your slicer, or in our STL to G-code slicer, which has simple vertical supports.
To change a hole diameter or a fillet radius, go back to the CAD model. A mesh only knows triangles. If you need the mesh inside CAD, STL to STEP writes a faceted body in which every triangle is a flat face. Expect about 1 KB per triangle; the result has not yet been checked by hand in desktop CAD.
Save the edited part and check it
Convert offers binary STL, ASCII STL and 3MF in millimetres. Pick 3MF when the next stop is a slicer that reads it, because 3MF records the unit; STL keeps bare numbers. STL to 3MF covers that choice in detail.
Before printing, read the size, volume and weight on the measure page. The editing runs in this browser tab. In the full test run every request went to the site's own origin, and nothing was posted. A longer walk-through lives in the guide how to edit STL files.
Questions and answers
Can I edit an STL file online without installing software?
Yes. The editor runs in a browser tab with nothing to install and no account. It is tested in Chromium browsers (Chrome 155); Firefox and Safari have not been tested yet.
How do I undo a change?
Press Undo at the top of the Edit panel. It keeps 20 steps, and Redo brings a step back.
Why does the tool ask me to run Repair first?
Booleans, cut and text need a watertight mesh. Run Edit → Repair, read what it fixed, then repeat the operation.
Can I change the diameter of a hole in an STL?
Not directly: the editor scales, rotates, cuts and combines whole meshes. Change the hole in the original CAD model, or subtract a cylinder file with A − B to widen it.
How large a model can I edit?
Memory is the limit. A model with 1M triangles opens in about 5–12 s; above roughly 1–2 million the tab may run out of memory. Reduce triangles first on the STL simplifier page.