JA4
JA4 fingerprints clients from TLS and HTTP header order — harder to spoof than user agent strings, and one of the strongest signals for bot detection.
What is JA4?
JA4 is a client fingerprinting technique that analyzes the structure and order of fields in TLS and HTTP headers. Unlike traditional methods that rely on user agent strings, JA4 examines how clients construct their requests, making it harder to spoof and more effective for identifying bots, malicious actors, and unique devices. It is widely used in security and fraud prevention.