Is Online CAD Conversion Safe? What Happens to Your Files

Search for “convert STEP to STL online” and you will find dozens of sites happy to take your file. Before you drop a design onto one of them, it is worth asking a simple question: where does the file actually go?

The standard model: upload, convert, hope

A conventional converter uploads your model to its server, runs a conversion job, and serves the result back. Your file — potentially a part under NDA, an unreleased product, proprietary tooling — now exists on infrastructure you know nothing about. Retention policies are vague when they exist at all; some services state outright that uploads may be kept to “improve the service”.

Why engineering data is special

A CAD model is not a holiday photo. It is often the intellectual property itself — the exact geometry a competitor would need. Many NDAs and export-control regimes (ITAR/EAR) flatly prohibit handing such data to uncontrolled third-party servers, and “I used a free converter site” is not an explanation any legal department wants to hear.

The alternative: convert where the file already is

Modern browsers can run real engineering software via WebAssembly. This site compiles the OpenCascade CAD kernel — the same kernel behind FreeCAD — to WASM and runs the entire conversion on your machine. The network tab tells the story: after the page loads, no file data leaves your browser. It works offline once loaded, and a 100 MB STEP file never spends a second on someone else’s disk.

How to verify a claim like this

• Open your browser’s developer tools → Network tab before converting.
• Drop the file and watch: a client-side tool sends no upload request.
• Disconnect from the internet and try again — client-side conversion still works.

Try it with the free converter or the 3D viewer — and keep your parts yours.