view server response

response body:

curl URL

response header (actual HEAD request):

curl -I URL

response header and body:

curl -i URL

to see request as well add -v, which adds extra info to stderr. to make -v output cleaner pipe stdout to /dev/null and suppress progress meter:

curl -vs URL > /dev/null

moar options:

-A 'user agent'
-u 'user:password'
-k, --insecure    don't check cert validity
-L  follow redirects

measure connection times

curl -s -w @.curl-format-times.txt -o /dev/null URL

timeout

php guzzle timeout ought () to be the entire libcurl transfer operation, which should include everything starting form name resolving, connection and data transfer. connect_timeout is only the first part. () according to someoine in the internet

proxy

http_proxy=<ip>:<port> curl <url>

view certificate

openssl s_client -servername DOMAIN -connect DOMAIN:PORT < /dev/null
openssl s_client -servername DOMAIN -connect DOMAIN:PORT < /dev/null 2> /dev/null | openssl x509 -noout -dates

-showcerts displays sent intermediate certificates as well.