How can I prove DualView never uploads my files?

Open your browser's DevTools Network tab, load two local files into DualView, compare them, and create a self-contained share link. You will see no upload requests: no POST or PUT carrying your file content. The only network traffic is the static app itself, because all comparison runs locally in your browser.

If nothing is uploaded, how do DualView share links work?

Share links carry comparison state (mode, slider position, time, labels) as query parameters, plus either https URLs of media you already host or the content itself compressed into the URL fragment after the # character. Browsers never send URL fragments in HTTP requests, so even self-contained links transmit nothing to any server.

Privacy Proof

Verify DualView's Privacy Yourself

Every comparison tool says it's private. DualView's claim is different in one way: you can falsify it in about two minutes with the tools already built into your browser. No file you open in DualView is ever uploaded, including when you create a share link. Here is how to check, not trust.

Open DualView Read the architecture docs

The Two-Minute Test

Open DevTools. In Chrome, Edge, or Firefox press F12 (or Cmd+Option+I on macOS) and select the Network tab. Check "Preserve log" so nothing scrolls away.
Load the app. Go to dualview.ai. You will see the normal static requests every website makes: HTML, JavaScript, CSS, fonts, icons. This is the app itself downloading to your machine. Once it has loaded, you can optionally filter the Network tab to show only Fetch/XHR requests to make the rest of the test easier to read.
Load two files. Drag two images or videos into DualView, including something large. Watch the Network tab: nothing happens. The files are read locally with the browser's File API and never leave your machine.
Compare. Drag the slider, switch modes, turn on metrics (Shift+M), scrub the video. Still nothing. SSIM, PSNR, heatmaps, and scopes are all computed in your browser.
Create a self-contained share link. Open the Share dialog and generate a content-in-URL link. Watch the Network tab as you do it: zero requests. There is no upload step because the link is the payload.
Go further if you like. Disconnect from the network entirely after the app loads and repeat steps 3-5. Everything still works, which is only possible because nothing depends on a server.

How a Share Link Can Carry a Comparison Without Uploading

A DualView share link has two kinds of cargo, and neither is an upload. Query parameters (?mode=slider&sp=35&la=Before&lb=After&a=...&b=...) carry comparison state and, optionally, https URLs of media you already host somewhere. For small content, the link instead carries the files themselves, compressed and encoded after the # in the URL (#dv=...).

The fragment detail matters: by the HTTP standard, browsers never send the part of a URL after # in any request. So even when a link literally contains your image, that content travels only inside the link you choose to send, person to person, and is decompressed by the recipient's browser locally. DualView's server (a static file host) never sees it. The full schema is documented in the URL parameters reference.

For comparisons too large for a URL, DualView exports a self-contained offline HTML file: a single document with the comparison embedded, which you can email or archive and open with no network connection at all.

How Upload-on-Share Tools Differ

Many comparison tools are genuinely local while you compare, but switch to uploading the moment you share. That is not necessarily wrong, hosted links have real conveniences, but it changes who holds your files, and it is worth knowing before you click share. The pattern is recognizable by its symptoms: file-size caps, link expiry dates, and per-account link quotas all exist because a server somewhere is storing your files.

A concrete example, as of June 2026: TwinLens compares files locally, like DualView, but creating a TwinLens share link uploads your files to TwinLens servers, with a 50MB cap per share, 14-day link expiry, and 5 share links on the free tier. imgsli likewise works by uploading images to its server, where comparisons are publicly accessible. Verify current behavior on twinlens.app and imgsli.com, and see our full comparisons: DualView vs TwinLens and DualView vs imgsli.

DualView's share links have no size cap from an upload service, no expiry, and no quota, because there is no upload and no server-side storage to limit. The trade-off is honest too: very large media cannot fit in a URL, so for those you either share the media URLs you already host (the a/b parameters) or use the offline HTML export.

Run the Same Test on Any Tool

This test is not DualView-specific, and we encourage you to run it everywhere: open the Network tab in any comparison tool, load a file, and click share. If you see a POST or PUT request with a payload about the size of your file, your file was just uploaded. Tools should earn the word "private" in the Network tab, not in marketing copy.

Sources Checked

Competitor details on this page reflect research as of June 2026 and can change; verify on twinlens.app and imgsli.com. DualView's own behavior needs no source: reproduce it in DevTools using the steps above. If anything here is out of date, tell us and we will correct it.