User-Agent Spoofing
User-Agent spoofing means making a browser report a different user-agent string than the real browser or device would normally send. The User-Agent is a short text that browsers include when they connect to a website (the User-Agent HTTP header) and it’s also available to page scripts via navigator.userAgent
. Because servers and anti-bot systems use the User-Agent for content negotiation and as one signal in fingerprinting, changing it is a common way to make a virtual profile look like a specific browser or device.
How sites use the User-Agent for fingerprinting & detection
- Signal in a bigger fingerprint: The User-Agent helps identify browser name, version, and OS. Trackers combine it with many other signals (screen size, platform, fonts, TLS/network traits) to more reliably identify devices.
- Inconsistency looks suspicious: If the User-Agent claims “iPhone Safari” but other signals (window size, navigator.platform, WebGL, TLS ciphers) look like a desktop, anti-bot systems treat that mismatch as a red flag.
- Client vs. server side reading: The UA string can be read both by the server from the HTTP User-Agent header and by JavaScript in the page from
navigator.userAgent
. Effective spoofing should keep both consistent.
Limits & risks
- Not a silver bullet: Changing the User-Agent alone is often insufficient - modern anti-bot systems use many signals.
- Stability vs. detection: Frequent or unrealistic UA switching may make profiles more detectable.
- Legal & policy issues: Spoofing can violate some sites’ terms of service; use responsibly.
HowKameleo addresses it
Kameleo helps by providing users with access to an unlimited pool of real, coherent fingerprints generated from the analysis of millions of samples. Instead of manually editing fields, users simply select a fingerprint where the User-Agent is already consistent with all other attributes. This ensures realistic, reliable profiles that detection systems are less likely to flag.
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