What Data Does Your Browser Leak? A Complete Privacy Guide

Every time you visit a website, your browser shares a surprising amount of information — even before you click anything or log in. This data is accessible through standard browser APIs and HTTP headers, and most of it is shared without asking your permission.

Here is what websites can typically see:

• Your IP address (and thus your approximate location, ISP, and connection type)
• Your browser name, version, and operating system
• Your screen resolution and window size
• Your timezone and language preferences
• Your installed plugins and fonts
• Whether you're using a VPN, proxy, or Tor
• Your WebRTC local IP (potentially revealing your real IP behind a VPN)
• Your battery status (on some mobile browsers)
• Your hardware specifications (GPU, CPU core count, memory)

You can check exactly what your browser reveals right now using LookMyIP's Privacy Check tool at lookmyip.com/privacy-check.

Your IP address is the most obvious piece of identifying information you share with every website. It reveals:

• Approximate location: Typically accurate to the city level (within 25-50 miles)
• ISP: Your Internet Service Provider
• Connection type: Whether you're on a residential, business, or mobile connection
• ASN: The network your traffic routes through

WebRTC leaks are a particularly sneaky problem. WebRTC (Web Real-Time Communication) is a browser technology used for video calls and peer-to-peer connections. It can expose your real, local IP address even when you're using a VPN, because it queries your network interfaces directly.

LookMyIP automatically detects WebRTC leaks and warns you if your real IP is exposed while using a VPN.

How to prevent IP leaks:

• Use a VPN to mask your public IP
• Disable WebRTC in your browser (Firefox: set media.peerconnection.enabled to false in about:config)
• Use browser extensions like WebRTC Leak Prevent or uBlock Origin

Browser fingerprinting creates a unique identifier for you based on the combination of your browser and system characteristics. Even without cookies, a website can identify you with high accuracy.

Key fingerprint components:

• Canvas fingerprinting: Websites draw invisible images using HTML5 Canvas. Tiny differences in how your GPU renders these images create a unique hash.
• WebGL fingerprinting: Similar to canvas but uses 3D graphics rendering, which varies by GPU model and driver version.
• Audio fingerprinting: Processing audio through the AudioContext API produces device-specific variations.
• Font enumeration: The set of fonts installed on your system is surprisingly unique.
• Screen and window properties: Resolution, color depth, pixel ratio, and window size.
• Navigator properties: Timezone, language, platform, hardware concurrency (CPU cores), device memory.

Studies show that browser fingerprints are unique for over 90% of users. Even if you clear cookies, your fingerprint remains the same — making it a powerful tracking mechanism.

Protection:

• Firefox with Enhanced Tracking Protection resists fingerprinting
• Tor Browser standardizes fingerprint characteristics across all users
• Brave Browser includes built-in fingerprint randomization
• Extensions like CanvasBlocker can spoof canvas fingerprints

First-party cookies are set by the website you're visiting. They're generally useful — keeping you logged in, remembering preferences, maintaining shopping carts.

Third-party cookies are set by external domains (ad networks, analytics services, social media widgets) embedded in the page you're visiting. These enable cross-site tracking — following you across different websites to build a browsing profile.

Major browser changes:

• Safari and Firefox already block third-party cookies by default
• Chrome has been working toward phasing them out (with Privacy Sandbox as a replacement)
• Many tracking services have adapted by using first-party cookies via CNAME cloaking or server-side tracking

Beyond cookies: Even if you block all cookies, trackers use fingerprinting, local storage, IndexedDB, ETags, and other storage mechanisms to persist identifiers. True privacy requires a multi-layered approach.

Level 1 — Basic (easy, minimal inconvenience):

• Use a modern browser with tracking protection (Firefox, Brave, or Safari)
• Install uBlock Origin ad/tracker blocker
• Use a reputable VPN service
• Check your exposure with LookMyIP's Privacy Check tool

Level 2 — Enhanced (some inconvenience):

• Disable WebRTC in browser settings
• Use Firefox with strict Enhanced Tracking Protection
• Use a privacy-focused search engine (DuckDuckGo, Brave Search)
• Clear cookies regularly or use container tabs (Firefox Multi-Account Containers)
• Disable JavaScript on sites that don't need it (NoScript extension)

Level 3 — Maximum (significant inconvenience):

• Use Tor Browser for sensitive browsing
• Use Tails OS for maximum anonymity
• Disable JavaScript by default
• Use separate browser profiles for different activities
• Avoid logging into any accounts while browsing anonymously

The right level depends on your threat model. For most people, Level 1–2 provides excellent privacy without breaking their browsing experience.