Last updated 10 September 2026.
What the extension collects
Nothing. It has no analytics, no telemetry, no crash reporting, and no server of its own. Nothing about you or the pages you visit is sent anywhere.
What it stores
Two kinds of settings, and only settings:
- Your preferences — the diff threshold, whether the outline is drawn, which frame was shown last, and whether the before / after / diff switcher is visible. They are kept by the browser's own extension storage. If you are signed into the browser and have extension sync turned on, the browser may sync them across your devices; that is the browser's mechanism, not ours.
- The permission you grant — held by the browser itself, and revocable at any time from the browser's extension settings.
No image, file name, repository name, URL, or account information is stored. Your settings — the threshold, the interface language, the colours of the difference, the addresses of your own instances — are kept by the browser and travel only through its own sync, if you have it on.
What it accesses
The extension runs on two addresses:
https://viewscreen.githubusercontent.com/diff/img, the frame
GitHub uses to display image diffs, and https://gitlab.com,
where GitLab renders them on the page itself. There it reads the two images
the site has already loaded and compares them in your browser. It does not
run on github.com pages, does not read your repositories, and
does not touch any other site.
The comparison happens entirely on your machine. The images never leave it.
If you add a GitLab or a GitHub Enterprise of your own on the settings
page, that instance's address joins the list — you grant it by hand, one host
at a time, and revoke it from the same page or from the browser's own
settings. A GitHub Enterprise is granted together with its
viewscreen subdomain, where GitHub draws the preview. The
extension behaves there exactly as it does on gitlab.com and on
github.com, and on a page with no image diff on it it does
nothing at all.
This page
The comparison page on this site works the same way: the images you drop there are read by the browser and never uploaded. There is no server behind the page — it is a static file on GitHub Pages.
What you set under Tune the comparison — the interface language,
the colours of the difference, the stitching, the threshold, the outline and the
last frame shown — is kept in the browser's own localStorage for
this page. It never leaves the browser, and clearing the site's data removes
it. No image, file name or size is stored.
Third parties
None. No data is shared, sold, or transferred to anyone, and no code is loaded from a remote server — everything the extension runs ships inside the package.
Contact
Questions and reports: the issue tracker.