What websites can see about your browser, and how to limit tracking
See what any website can read from your browser: screen size, time zone, cores and privacy signals. Based on Mozilla and EFF guidance; nothing leaves this page.
- Run the checkIt reads what this browser tells every website, right here, without sending anything.
- See your exposureEach signal is marked: what a site can read and how much it narrows you down.
- Close the gapsFollow the settings and tools listed for each signal to share less.
Official source: EFF, What Is Fingerprinting?. Verified on
Sites can recognise a browser without cookies by combining small details such as screen resolution, time zone and operating system version, and because that fingerprint is not stored on your device, there is nothing to delete (EFF). The check above shows the details your browser hands to every page. It cannot say whether your combination is unique; the EFF's Cover Your Tracks compares you with its own data set for that.
Each line of the result, and what to do about it
| Line in the result | Why it matters | What changes it |
|---|---|---|
| Global Privacy Control | A legal opt-out request in California, Colorado, Connecticut and some other places (Mozilla) | Turn it on in two minutes, then rerun the check |
| Do Not Track | The older request; Firefox removed it in version 135 (Mozilla) | Nothing needed; GPC replaces it |
| Screen size, window size | Classic fingerprint inputs; Tor Browser rounds the window to steps of 200 × 100 pixels (Tor Project) | Tor Browser, Safari Private Browsing |
| Time zone, languages | Stable, and they give away your region even behind a VPN | Does a VPN stop it? |
| Processor cores, touch points | Firefox's protection reports cores as 4 or 8 and touch points as 0, 1 or 5 (Mozilla) | Firefox fingerprinting protection |
Run it once in a normal window and once in a private or protected one: the lines that change are the ones that browser is masking.
Questions people ask next
- What exactly is fingerprinting, and which techniques does it use? What it is and how it works, with the arithmetic of how unique a browser is.
- What actually reduces it? Which defence answers which technique, then a ticked privacy plan for your browser.
- Does private mode help? Incognito and fingerprinting.
- How do the browsers compare? Side by side, then Chrome, Edge, Brave and Google's 2025 policy change.
- What about tracking in links? Clean one link with the parameter cleaner or a whole newsletter with the batch cleaner.
- What does the law say? EU rules, GPC and California, what the GPC signal is, and the FAQ.
Independent site: Mozilla, the EFF and the browser makers did not write or review it. Features differ by browser version, so each page carries the date we read its source.