STEP viewer online
Open STEP files instantly — measure in mm, cut a section, spot overhangs and check if the model is ready to print. Nothing is uploaded.
What is a STEP file?
STEP, formally ISO 10303 and known as the Standard for the Exchange of Product model data, has been developed since the 1980s and is the main neutral format for moving CAD models between companies and systems. The usual application protocols are AP203 and AP214 for geometry and assemblies, and AP242 for modern product and manufacturing information. A .step or .stp file is plain text written in the EXPRESS-based Part 21 syntax. Unlike STL, it does not store triangles: it stores boundary representation (B-rep) geometry, meaning exact planes, cylinders, splines and NURBS surfaces joined by edges and faces into solids. That keeps holes perfectly round and dimensions precise, and allows the receiving CAD to keep editing faces. Files can contain assemblies, product structure, colours and units.
What a STEP file can store
A STEP file stores exact B-rep geometry: analytic surfaces, NURBS patches, curves, edges, faces and closed shells that form solids. It can also hold assembly structure with part names and placements, length units declared in the file, and surface colours and layers in common application protocols. AP242 adds tolerances and annotations. Parametric history, such as sketches and feature trees, is not part of a STEP file, so a receiving CAD sees solids, not the recipe that built them.
Apps that open STEP
SolidWorks, Fusion, Onshape, FreeCAD, Autodesk Inventor, Siemens NX, CATIA, Creo, Rhino, OpenCascade-based tools.
Strengths
- Exact surfaces rather than a triangle approximation
- Accepted by essentially every commercial CAD package
- Carries assemblies, units and often colours
- Stable ISO standard used for long-term archives
Limits
- Slicers generally cannot open it; it must be meshed first
- No feature history or editable sketches
- Files from different CAD systems can have translation errors
- Large assemblies produce heavy text files
STEP and 3D printing
Most slicers cannot read STEP, though some, like PrusaSlicer, will import it and mesh it internally, so the usual step is exporting STL or 3MF from your CAD program. Tessellation quality decides how smooth the printed curves look: too coarse and cylinders become visible facets, too fine and files grow huge. MeshShift reads STEP and STP using OpenCascade in the browser and lets you pick draft, normal or fine tessellation. When it writes STEP, the result is a faceted B-rep: a solid made of flat triangular faces, not a parametric CAD model, so it will not give you editable holes or fillets. Use it to exchange a mesh as a solid, not to recover design intent.
Frequently asked questions
How do I open a STEP file without installing software?
Drop the STEP file on this page. It opens in your browser with studio lighting and real dimensions; nothing is uploaded. You can rotate, zoom, measure between two points, cut through the model and check whether it is watertight for printing.
What is the difference between STEP and STP?
Nothing in the content. Both extensions hold the same ISO 10303 Part 21 text; .stp exists because older systems limited extensions to three letters. Any program that reads one reads the other, and renaming the file is enough.
Why does my STEP file look faceted after conversion to STL?
STEP stores exact curves, and STL can only hold triangles, so the converter has to approximate them. Choose a finer tessellation setting to get smoother cylinders and fillets, at the cost of more triangles and a larger file.
Can MeshShift turn an STL into an editable STEP model?
No. MeshShift can write STEP, but the output is a faceted B-rep, a solid made of flat triangle faces, not a parametric model with real cylinders or features. It is useful for importing a mesh into CAD as a solid. Reading STEP and converting it to STL or 3MF works in the browser.