P0F OS Fingerprint Checker
Check what your TCP/IP fingerprint reveals about your operating system. Detect VPN/proxy usage and OS mismatches.
Passive OS Fingerprinting
When you connect to any website, your OS kernel sends a TCP SYN packet with unique default values. This tool analyzes those values to determine your operating system — no software to install, no probes sent to your device.
Your browser must already be connected to our server for the fingerprint to be captured.
About P0F OS Fingerprint Checker
P0F OS Fingerprint Checker is a free online tool that check what your tcp/ip fingerprint reveals about your operating system. detect vpn/proxy usage and os mismatches.. No registration or software installation required — simply upload your file, adjust settings, and download the result.
How to use P0F OS Fingerprint Checker
- Upload your file file using the upload area above
- Adjust processing options as needed
- Click "Process" and wait for processing
- Download your result file
Key Features
- 100% free with no daily limits
- No registration or account needed
- Files automatically deleted after 30 minutes
- Processed entirely in your browser — nothing leaves your device
Frequently Asked Questions
Everything you need to know about this tool
P0F (Passive OS Fingerprinting) is a technique that identifies your operating system by analyzing the TCP/IP packets your device sends. Different OS kernels use different default values for TTL, window size, TCP options order, and other fields — creating a unique fingerprint.
Yes. When you connect to any website, your device sends a TCP SYN packet to establish the connection. The server can analyze this packet's fields (TTL, window size, TCP options) to determine your operating system without sending any probes back to you.
A mismatch between your TCP/IP fingerprint and your User-Agent header usually indicates that your connection is routed through a proxy or VPN. The proxy's operating system (typically Linux) replaces your actual TCP fingerprint, while your browser still sends the original User-Agent.
Your TCP fingerprint is determined by your operating system kernel and cannot be changed through browser settings. Advanced tools like OSfooler-ng can modify outgoing packets on Linux, and some anti-detect browsers normalize fingerprints through their proxy infrastructure.
No. This tool is completely passive. It only analyzes the TCP SYN packet that your browser naturally sends when connecting to our server. No additional packets are sent to your device.
The VPN/Proxy hint checks your Maximum Segment Size (MSS) value against known patterns. VPN protocols like IPsec, OpenVPN, and WireGuard reduce the MSS due to tunnel encapsulation. An MSS of 1300-1400 instead of the standard 1460 suggests a VPN connection.