As a high school teacher, I've seen firsthand the effects that a lack of privacy has on creativity, freedom of expression, and willingness to mess up. I don't think we should be subject to consistent monitoring and told we be okay with it "if we have nothing to hide." This is why, between grading and lesson planning, I built 404.

Without 404, your browser and network advertise dozens of semi-unique values: screen size, browser version, hardware stack, installed fonts, TLS handshake pattern. Individually, none of them are remarkable. Combined, they form a fingerprint specific enough to recognize your device across sessions, sites, and networks. It doesn't matter if you're using a VPN or if you clear your cookies. Your IP changes, but everything else stays the same. This is browser fingerprinting, and the industry built around it is called identity resolution.

404 replaces your device fingerprint with a believable alternative so that the browsing you want to be private can actually be private. Where a VPN replaces your IP address, 404 replaces the device behind the request.

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404 is a localhost TLS-terminating proxy available as a binary or 2-click install desktop app. It rewrites your TLS handshake, HTTP headers, and JavaScript surfaces to match a single internally consistent device profile, verified against real fingerprinting services. All of this runs locally on your machine. 404 hosts no infrastructure, handles no traffic, and has no access to your data.

Currently spoofing all values tested by BrowserLeaks. With a VPN, FingerprintJS and DataDome report a different user.

The proxy (STATIC) is open source under AGPLv3. The desktop app is a licensed GUI wrapper that builds directly from source. Happy to answer questions in the comments.

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Use LAUNCH01 for two months free. App: 404privacy.com

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Code: github.com/un-nf/404 Docs: un-nf.github.io/404-docs

Notes: On GitHub, you will also find an eBPF module built for mutating tcp/ip fingerprinting values. This covers fingerprinting values collected by tools such as nmap or p0f that can be used to identify your OS. This is not yet worked into the application as it requires a Linux kernel.

Wrapping the proxy and eBPF in a mini-kernel that can run on WSL2 or Docker is coming soon!

user:	qcoudeyr
created:	March 5, 2026
karma:	2