How to check TLS version of a website

Run curl -sI https://example.com/ -o /dev/null -v 2>&1 | grep 'SSL connection'. The line reads SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384, and the first field is the version this connection negotiated. Read the version from that field, never from the cipher name printed beside it.

Why check this

This check answers one question: which protocol version did the client and the server settle on right now. It runs after any change to a load balancer, a CDN setting or a reverse proxy, because a proxy in front of an updated origin can pin the connection to an older version than the origin supports. A payment integration that requires TLS 1.2 or higher fails the day a terminating proxy starts answering in TLS 1.1, and the application log shows a connection reset with no protocol detail.

Which version was negotiated is a different fact from which versions the server offers. This page covers the negotiated one. For the offered set, run the sweep in How to test SSL configuration.

Prerequisites

• curl 7.52 or later. Any TLS backend works. See the curl manual.
• OpenSSL 1.1.1 or later for s_client, documented in the s_client manual.
• Node 18 or later for step 3. Its TLS stack reports the negotiated version through a separate API, which is what makes it a useful cross-check.

Steps

1. 1

   Step 1.

   Ask curl to print the connection summary and keep the one line that names the version.

   curl -sI https://www.cloudflare.com/ -o /dev/null -v 2>&1 | grep 'SSL connection'
   

   * SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384 / [blank] / UNDEF

   The first field after using is the protocol version. The second is the cipher suite. The two are separate facts.

2. 2

   Step 2.

   Read the same value from a different TLS stack, so a single client's reporting quirk cannot mislead you.

   node -e "require('node:tls').connect({host:'www.cloudflare.com',port:443,servername:'www.cloudflare.com'},function(){console.log(this.getProtocol());this.end()})"
   

   TLSv1.3

   getProtocol() returns the negotiated protocol and nothing else, so there is no field to misread.

3. 3

   Step 3.

   Force an old cipher suite on a modern server and compare what each tool prints. This is the trap the next section explains.

   openssl s_client -connect www.cloudflare.com:443 -servername www.cloudflare.com -tls1_2 -cipher 'AES128-SHA@SECLEVEL=0' </dev/null 2>&1 | grep '^New,'
   

   New, SSLv3, Cipher is AES128-SHA

   The connection is TLS 1.2. Node reports TLSv1.2 AES128-SHA SSLv3 for the same handshake, which shows that SSLv3 here is an attribute of the cipher.

How to read the result

| What you see | What it means | What to do | | --- | --- | --- | | SSL connection using TLSv1.3 | The handshake used TLS 1.3 | Nothing. Record it in the release notes. | | SSL connection using TLSv1.2 | TLS 1.2 was the highest both sides agreed on | Check whether the server offers 1.3 and the client refused it, or the reverse. | | SSL connection using TLSv1.0 or TLSv1.1 | A deprecated version is live | Treat as a release blocker. RFC 8996 deprecates both. | | New, SSLv3, Cipher is AES128-SHA | The cipher dates from SSL 3.0 | Ignore this field for versions. Get the version from step 1 or step 2. |

Common mistakes

What to check next

• How to check if a website supports TLS 1.3: what the server can do, which is not what it did on your connection.
• How to check if TLS 1.0 is disabled: the negative test, and why a refusal is easy to fake.
• How to check cipher suites of a server: the second field on the same line, read properly.
• How to test SSL configuration: the sweep that covers versions, ciphers and the certificate in one pass.
• SSL certificate checker: the versions offered and the chain, without a shell.

FAQ

How to check TLS version in Linux?

The same two commands. curl and OpenSSL ship on every mainstream distribution, and curl -v prints the SSL connection using line identically on Linux, macOS and Windows. No distribution specific tool is needed.

How to check TLS version with nmap?

nmap --script ssl-enum-ciphers lists every version a server offers. It answers the offered question, not the negotiated one, and it opens one connection per version and cipher. The commands above use one connection and need no extra install.

Does the browser padlock show the TLS version?

Chrome shows it under DevTools, Security tab, in the Connection section. That value is the browser's negotiated version, which can differ from curl's if the browser and curl disagree on supported versions.

Why does a server offer TLS 1.3 but negotiate 1.2?

The client did not offer 1.3. Old OpenSSL builds, Java 8 before update 261 and some corporate TLS proxies cap the client at 1.2, and the server takes the highest both sides list.

Verified