Font Fingerprint
See which fonts a site can detect on your machine, and why that identifies you.
How this test works
No browser will hand a page a list of installed fonts. What a page can do is measure a string rendered in a candidate font and compare the width against the same string in a generic fallback — if they differ, the browser found the font; if they match, it fell back. Repeating that across a list of candidates reconstructs which fonts are present. The set is identifying because installed fonts follow installed software: a machine with a design suite, or a particular set of language packs, or a game's bundled fonts, carries a distinctive trail. This page probes a modest list, shows what it found, hashes the set and discards it.
What the results mean
- Fonts detected
- How many of the probed candidates measured differently from the fallback.
- A low number
- Usually a browser restricting font access rather than a sparse machine. Safari and the Tor Browser both do this.
- The list shown
- Rendered in the fonts themselves, so you can see the detection was real rather than asserted.
- Font hash
- A digest of the detected set. What a tracker would actually store.
Common problems and fixes
- It found very few fonts
- Almost certainly a browser restricting access to a fixed system list, which is the outcome you want. Safari and the Tor Browser both behave this way.
- It missed a font I definitely have
- The probe uses a fixed candidate list rather than enumerating. A font not on the list cannot be found, and metric-compatible fonts can measure identically to their fallback.
- Why does my font list identify me?
- Because fonts arrive with software. A design suite, a language pack or a game each leaves a distinctive set, and the combination is often rarer than people expect.
Frequently asked questions
Can a website see all my fonts?
No — not directly. It measures candidates against a fallback and infers which ones exist, so it can only find fonts it thinks to ask about. The effect is similar but the mechanism matters, because it means the list is bounded.
Why are installed fonts so identifying?
Because they track installed software rather than hardware. Two people with the same laptop model usually have different font sets, and the combination narrows a population quickly.
How do I reduce this?
Use a browser that restricts font access to a fixed system list — Safari and the Tor Browser both do. Uninstalling fonts is not worth doing for this reason alone.