JA4 is a TLS client fingerprint format that hashes sorted cipher suites and TLS extensions into a stable string. The protocol segment (for example t13d1516h2) indicates TLS 1.3, SNI usage, cipher count, extension count, and negotiated ALPN such as HTTP/2.
Node.js HTTP clients often produce JA4 values that differ from real Chrome even when the User-Agent header matches Chrome. See the JA4+ spec (FoxIO) and capture baselines on tls.peet.ws.
Decode JA4 strings with the free JA4 Decoder or browse Fingerprinting Resources.