hey @Alan, you can use the check_http plugin for this purpose. It monitors response time, error codes, server certificates and much more. 
The commands.cfg file contains a comman defination for using the check_http plug-in. Something like this:
define command {
    name            check_http
    command_name    check_http
    command_line    $USER1$/check_http -I $HOSTADDRESS$ $ARG1$
}
A simple service definition for monitoring the HTTP service on the host machine might look like this:
define service {
    use                 generic-service     ; Inherit default values from a template
    host_name           remotehost
    service_description HTTP
    check_command       check_http
}