Curl: one-liner to test http/2 support

Run

curl --version

and look for HTTP2 on the Features list

Here you can find a list of Tools for debugging, testing and using HTTP/2.

Probably the easiest one from the command line is:

$ is-http2 www.cloudflare.com

But that requires npm install -g is-http2-cli

For testing using curl you may need to compile it using the nghttp library, in macOS this can be done by using brew you could use:

$ brew install curl --with-nghttp2

And then you could use what @daniel-stenberg suggests in his answer

$ curl -sI https://curl.haxx.se -o/dev/null -w '%{http_version}\n'

In where you will get a 2 if http2 is supported.

HTTP/2 supported:

$ curl -sI https://curl.se -o/dev/null -w '%{http_version}\n'
2

HTTP/2 not supported (instead serving 1.1 in this case):

$ curl -sI http://curl.se -o/dev/null -w '%{http_version}\n'
1.1

(curl 7.50.0 or later is required for this command line to work)