[runjake]

If you want super minimal, something like this might work?

  #!/bin/bash

  # Add this script to cron to run at whatever duration you desire.

  # URL to be checked
  URL="https://example.com/test.php"

  # Email for alerts
  EMAIL="[e-mail]"

  # Perform the HTTP request and extract the status code with 10 second timeout.
  STATUS=$(curl -o /dev/null -s -w "%{http_code}\n" --max-time 10 $URL)

  # Check if the status code is not 200
  if [ "$STATUS" -ne 200 ]; then
      # Send email alert
      echo "The URL $URL did not return a 200 status code. Status was $STATUS." | mail -s "URL Check Alert" $EMAIL

      # Instead of email, you could send a Slack/Teams/PagerDuty/Pushover/etc, etc alert, with something like:
      curl -X POST https://events.pagerduty.com/...
  fi

Edit: updated with suggested changes.

[divbzero]

As a slight variation, you could send an alert to the PagerDuty API by replacing “Send email alert” with something like:

  # Send PagerDuty alert
  curl -X POST https://events.pagerduty.com/...

[runjake]

Added.

In fact, this is what I'd recommend (though I use Pushover), because then you don't have to be concerned with email setup, not getting caught in spam filters, firewalls, etc. You could also send a Slack/Teams alert with a similar POST.

For some reason, I thought I had read that OP wanted to send an email.

[zikduruqe]

Or apprise for a whole bunch of notifications.

https://github.com/caronc/apprise

[drivers99]

You should include a timeout in the curl to detect if it hangs, or if it gets slower than it should be.

[runjake]

Added!