Script to ping URLs defined in urls.txt and alert you if they do not return 200 OK. You'll need to `sudo apt-get install bsd-mailx` to get the email, and you'll want to add a filter to make sure that $from is never sent to spam. A log is also kept in log.txt including timestamp, status code, and URL.

crontab

*/5 * * * * /home/pi/pinger/pinger.sh > /dev/null 2>&1

pinger.sh

#!/bin/bash                                                                                                         

from="pinger@raspberrypi.local"
to="username+pinger@gmail.com"
timeout=60

cd $(dirname $0)

function ping_url {
    url=$1
    url_hash=$(echo $url | md5sum | awk '{print $1}')
    response_file=/tmp/pinger-response-${url_hash}
    status_file=/tmp/pinger-status-${url_hash}

    status=$(curl -s -S -i -m $timeout --stderr $response_file -o $response_file -w "%{http_code}" $url)
    echo -e "\nURL: $url" >> $response_file
    if [ -e $status_file ]; then
    last_status=$(cat $status_file)
    fi
    if [ $status != 200 ] && [ $status != $last_status ]; then
        mailx -s "Ping status $status for $url" -a "From: Pinger <$from>" $to < $response_file
    fi
    if [ ! -z "$last_status" ] && [ $last_status != 200 ] && [ $status == 200 ]; then
	mailx -s "Ping status $status for $url EOM" -a "From: Pinger <$from>" $to < /dev/null
    fi
    echo $status > $status_file
    echo $(date "+%Y%m%dT%H%M%S") $status $url | tee -a log.txt
}

for url in $(cat urls.txt); do
    ping_url $url &
done

urls.txt

http://www.example.com/foo.html
http://www.example.net/bar/baz/