RedFlag is a free tool that allows users to mark any link with up to three different content warnings and provides a link to use in the original link’s place. The new link displays the selected warnings so viewers can choose whether they want to see the content or not. Using the generated link on social media will instead display a red screen with warning text in the link preview instead of any potentially harmful images on the target link. It also provides a way to add your own warnings if the one you are looking for is not on the included list, but it only sticks around if more than one person uses the same warning in a set period of time.
It is built with PHP, jQuery, and SQLite, and it is open source on GitHub.