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What "processed in your browser" really means

Updated 25 September 2026

Every tool on gratistools.be does its work inside your browser tab, with JavaScript and WebAssembly. Here's what that means in practice.

How it works

When you open a tool page, your browser downloads the program — the same way it downloads any web page. When you choose a file, the browser reads it from your disk into the tab's memory; the tool processes it there and hands the result back as a download. The file is never sent over the network. PDF work uses established open-source engines (pdf.js from Mozilla, pdf-lib, and qpdf compiled to WebAssembly); images are decoded and encoded by your browser itself.

What it protects

  • Your files can't leak from our servers, because they never reach them — there's nothing to breach, subpoena or accidentally log.
  • No retention questions: there's no "we delete files after one hour" to trust.
  • Sensitive inputs — contracts, bank statements, API tokens, passwords for a PDF — stay on your device.

What it doesn't protect

  • Your own device. Malware or a compromised browser extension could read what you process. That's true for every app.
  • Saved items. If you sign in and press Save on a comparison, that comparison is stored in your account. Nothing else is.
  • Downloads. Once you download a result, it's an ordinary file on your device.

Check it yourself

Open your browser's developer tools (F12), go to the Network tab and use a tool. You'll see the page and its code load, and small anonymous usage counters (an event name and tool name, no content) — but no request containing your file or text.

Trade-offs

Processing happens on your hardware, so very large jobs (a 500-page scan, a 50-megapixel upscale) depend on your device's memory and speed. On the other hand there are no upload waits, no queues and no file-size paywalls.

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