How to check whether any online tool uploads your file
Open your browser's developer tools, watch the Network tab while you use the tool, and look for a request as large as your file. Or load the tool, switch off your connection, and try again. Both take two minutes and work on any site, including this one.
Updated 3 min read
The tool this guide uses
Drag files here, or
JPEG, PNG, WebP, AVIF and GIF. Decoded on your device, never uploaded.
Encodes at quality 76, tuned to be indistinguishable from the original at normal viewing size. This is the setting to use when you just want the file smaller.
Optional. Height follows automatically.
Ready. Runs locally on your device.
Your files stay on your device. The tool works directly in your browser, using your device to process your files. Nothing is sent to our servers, and we never receive, store, or see your files or figures.
On a computer: the Network tab
Every browser can show you each request a page makes. This is the most reliable test, and it takes two minutes.
- Open the tool’s page. Press F12, or right click the page and choose Inspect, then open the Network tab.
- Clear the list with the clear button, so only new requests will show.
- Use the tool with a file that does not matter, ideally one of a size you know, such as a 2 MB photo.
- Look at the list. For each request, compare the size of what was sent with your file.
What you are looking for:
- An upload shows as a request, usually a
POST, at least as large as your file, often to an address with “upload” in it. Its request payload will be your file, sometimes split into several parts. - A local tool makes no request carrying your file. You may see small requests, or downloads of the tool’s own code the first time, but nothing going out that is anywhere near your file’s size.
In Chrome and Edge, click a request and open Payload to see what was sent. In Firefox, the equivalent is the Request tab. In Safari, enable the Develop menu in Safari’s settings first, then open the Web Inspector.
You can try it right now on the image compressor above: compress a photo and watch the Network tab stay empty of anything your size.
On a phone: the airplane mode test
Phones do not make developer tools easy, but the offline test works just as well for a quick check.
- Open the tool and use it once with any file while you are online, so everything it needs has loaded.
- Turn on airplane mode.
- Use it again with another file.
If it still works, it does not need to send your file anywhere to do the job. If it stalls, spins, or reports a network error, the file was on its way to a server.
Reading what a site says
The test tells you what happens; a site’s policy tells you what it promises. It is worth reading both. Look for:
- Where files are processed: on their servers, or in your browser.
- How long files are kept: many services delete within one or two hours.
- Exceptions: some keep certain files longer, such as signed documents, for legal reasons.
- Who else touches them: hosting providers, sub-processors, and the country the servers are in.
A clear policy that matches what the Network tab shows is a good sign. A vague one, or none at all, on a site that clearly uploads your file, is a reason to use something else for anything personal.
What this site does
Every tool on Reembun works inside your browser, including the ones on this page, and that is a claim this test lets you check rather than take on trust. The tools do download their own engines the first time you use them, such as the PDF renderer or the text recognition data for a language, and those downloads can be several megabytes. Your file never goes the other way.
Common questions
Is uploading a file to an online tool always bad?
No. Many good services upload files, process them and delete them within an hour or two, and say so in their policies. What the test tells you is simply whether a copy of your file ends up on someone else's computer. For a birthday invitation that hardly matters; for an ID card or a contract it may.
Why do I see large downloads when I use a tool here?
Some tools here need an engine, such as the PDF renderer or the text recognition data for a language, and download it the first time you use them. Those are responses coming to you, not your file going out. The test looks at what is sent, not what is received.
Does the airplane mode test prove everything?
It proves the tool does not need to send your file to do its job. A tool could in principle wait and send data later, once you are back online, which is why the Network tab is the more thorough of the two tests.
Cite
Cite this page
Reembun. (2026, September 11). How to check whether any online tool uploads your file. https://reembun.com/guides/check-if-a-tool-uploads-your-file
About Reembun
Reembun is a free collection of more than 100 online tools for PDFs, images, video, audio, text and everyday calculations. Every tool runs inside your browser, so your files are processed by your own device and are never uploaded to a server. There is nothing to install, no account to create, and no watermark on what you make.
You do not have to take our word for it. Open your browser’s developer tools, watch the Network tab, and use any tool: your file never appears there.
Reembun is built and run by PT RHP Cipta Digital, a registered company in Indonesia.
