What can a website see from one request?
Before any page loads, the server already has your IP address and port. Public databases turn the IP into a city, a country, an ISP or hosting company and an autonomous system number (ASN), and lists say whether it is a known VPN, proxy, datacenter or Tor exit. The first packet of the connection, the TCP SYN, carries a TTL, window size and option order that differ by operating system. The TLS handshake lists ciphers and extensions in an order that identifies the browser or library. The HTTP headers add language, User-Agent and client hints.
What is a TLS fingerprint (JA3, JA4)?
When your browser opens an HTTPS connection, it sends a ClientHello: supported TLS versions, cipher suites, extensions, elliptic curves and protocols such as HTTP/2. JA3 and the newer JA4 condense that list into a short string. Chrome, Firefox, Safari, curl and Python each produce a different one, so a script pretending to be Chrome is easy to spot. JA4H does the same for HTTP headers; the Akamai fingerprint for HTTP/2 settings.
How can a site know my operating system?
Through TCP/IP fingerprinting. Windows starts packets with a time-to-live of 128, Linux, Android and macOS with 64. Window size, maximum segment size and the order of TCP options narrow it further. Because this comes from the operating system's network stack, it cannot be changed by a browser setting, and a mismatch with the User-Agent is a strong hint of spoofing or a proxy.
What is a DNS leak?
Every website name you visit is looked up by a DNS resolver, usually your ISP's. If you use a VPN but name lookups still go to your ISP, your browsing is visible to them: a DNS leak. This page makes your browser resolve a unique name under our own DNS server and shows which resolver asked for it, and which network it belongs to.
What is a WebRTC leak?
WebRTC lets browsers make direct audio and video connections. To do that it asks a STUN server for your public address, which can bypass a proxy or VPN configured only in the browser and reveal your real IP. This page runs that test against its own STUN server and compares the result with the address of your request.
Does a VPN hide all of this?
A VPN replaces your IP address and location, and hides your traffic from your ISP. It does not change your browser's TLS fingerprint, your screen, fonts, graphics card, time zone or language. When those disagree with the VPN's location, for example a Tokyo IP with a Berlin time zone, sites can tell. The cross-checks on this page show exactly those contradictions.
What is browser fingerprinting?
Without cookies, a site can still recognise a browser by combining what JavaScript can read: screen size and position, GPU and canvas rendering, audio processing, installed fonts, time zone, languages, hardware threads and memory. Each detail is common; together they are often unique. Section 03 shows the attributes this page combined into your fingerprint ID.
Can I save or share the results?
Yes. Section 05 exports the whole report or any part of it as JSON, YAML, TOML, CSV, .env or Markdown, to copy or download. Every value shown on the page is in the export, with the same names.