TLS Client Hello Mirror

This service presents your browser's TLS Client Hello message in multiple formats. It can be used directly or in CI tests to check for TLS privacy pitfalls (session resumption, fingerprinting, system time exposure) and security shortcomings (deprecated TLS versions, weak cipher suites, missing features, etc). Details here.

API endpoints

API documentation


TLS session resumption marginally speeds up the initiation of connections, but it affects privacy in much the same way that HTTP cookies do: the server provides a unique token that your browser sends back on subsequent connections, allowing the server to link your visits even if your IP address changes. The browser can mitigate this by enforcing a short TLS session lifetime: the paper linked below proposes a limit of 10 minutes or less.

Tracking Users across the Web via TLS Session Resumption

Client Hello

Supported features

Supported TLS/SSL versions

Cipher suites


Supported groups

Signature algorithms

TLS fingerprint

Parameters in the Client Hello message differ between clients, enabling servers and on-path observers to detect what browser you are likely using (down to its version, or a range of versions) by deriving its fingerprint from said parameters. Worse, if you change any TLS-related settings, your TLS fingerprint becomes specific to a much smaller group of users, possibly even to you alone.

JA3 is a simple and popular type of TLS fingerprint. NJA3 is a similar style of fingerprint which aims to improve the robustness and accuracy of JA3.