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How it works and why your files never leave your device

Wololo has no conversion server. When you convert a file, your own browser does the work, and here is how you can check it.

What happens when you convert a file

When you open the page, your browser downloads the converter code from this site, just like any image or stylesheet. When you drop a file, that code reads it straight from your device, converts it in a separate process (a Web Worker) and offers you the result to download.

For formats the browser cannot handle, such as HEIC, AVIF, RAR, AVI or PDF manipulation, programs compiled to WebAssembly are used (libheif, qpdf, libarchive, ffmpeg…). They are also downloaded from this site the first time they are needed and run on your computer. Audio and video are encoded with the browser’s own codecs (WebCodecs), which are usually hardware-accelerated.

How to check that nothing is uploaded

You do not have to take our word for it: you can see it yourself.

  1. 1Open your browser’s developer tools (F12) and go to the “Network” tab.
  2. 2Convert a file. You will see that your file travels in no request: only files from this site are downloaded, and a statistics notice is sent with the conversion type and whether it worked, never the file name or content. If you accepted ads, you will also see Google’s requests.
  3. 3Or, simpler: load the page, turn on airplane mode and convert. It works the same, because converting needs no internet.

Security measures

A content security policy (CSP) prevents the site from loading code from other domains. The only exception is Google’s ad code, which is loaded only if you give your consent; the ads themselves are shown in isolated frames that cannot read the page. Generated HTML documents are cleaned of scripts and previews are shown isolated.

Archives are checked before extraction to stop “bombs” that expand to huge sizes, and file names are sanitised so nothing can be written where it should not.

Limits

Since everything happens on your device, its memory and processor set the limits. On a computer you can convert large files; on a phone the limits are lower and you are told before starting if a file does not fit.