Which free file tools upload your file? We measured 29 with Chrome's NetLog

By Venkat Dixit Kallepalli · Tested 10 November 2026 · 26 sites measured, 3 blocked the test

We merged two PDFs or compressed one photo on 26 free online tools, twice each, and recorded every byte the browser sent. The files were made for the test and carried a hidden marker, so a copy of the file could be recognised wherever it went.

The good news first: every site that says your file stays on your device kept that promise. The surprises were elsewhere: most sites that do upload start sending the file the moment you choose it, and several tool pages load session recording.

sites that promise the file never leaves your device kept the promise in every run

sites sent the file to a server, most of them saying so on the page

of those started the upload as soon as the file was chosen, before any button was pressed

tool pages loaded a session-recording script (Microsoft Clarity or Hotjar)

These sites blocked our automated test browser, so they are not in the results. We did not try to get around the block:

You can check any of them yourself in a minute: see “How can I check a site myself?” below.

Not by itself. Server tools encrypt the transfer and most delete files on a schedule, and some jobs need a server. It matters for documents you would not hand to a stranger, such as ID scans, contracts, bank statements and medical letters. For those, a tool that works in your browser avoids the question.

Open the browser developer tools (F12), go to the Network tab, then run the tool on a test file. Look for a request whose size is close to your file. On many sites it appears the moment you choose the file.

The 48 browser tools do not, and this test measured that for Merge PDF and Compress Image. Five conversions do use our server: Compress PDF, PDF to Word, Word to PDF, PDF to Excel and PDF to PowerPoint. Each says so on the page, and the file is deleted as soon as the result is sent back. We ran Compress PDF through the same test as a control, and it was detected as an upload, as it should be.

Tell us through the contact page with the site and what changed. We re-run the test, update the table and note the date of the change.

The full results are free to reuse under CC BY 4.0, with a link to this page: CSV and JSON. Each row has the site, job, verdict, upload destination, timing, session-recording scripts and other domains contacted.

Related: how to check whether a PDF tool uploads your files and how Drible handles files.