The Uptime Bot is a project that aims to take away the need to manually check if a site is up or down. Set it up once in the bot and receive a notification if the site is down. You can also run a command to check if a site is up without adding it to a schedule or getting it saved anywhere.
Upvote Uptime Bot
A bot that will check if a "monitor"(aka a website) is up and if it's down will send a message.
Check out the home page for the full Discord Bot List.