Foundry
There are a few extensions available for using 5etools in combination with Foundry. See them below.
To install the Plutonium module, and start using all of 5etools' content in your game, paste the manifest URL[current/v14/v13] into your Foundry server's module installer. See the Plutonium Features page for an overview of the functionality the module provides.
You can also install the Rivet browser extension (Chrome/Firefox) to import content from the site with a single click.
FAQ
Is there a wiki? Here. Contributions are welcome.
Browser and device support? The latest desktop versions of Chrome and Firefox.
Where's my stuff? There's no account system. Everything is stored in cookies. If you wipe those, or close your incognito window, it's gone forever. You can download your data for safekeeping via the Settings menu.
Other versions? A "current" version is available.
Anything else I should know? Hold SHIFT when hovering to lock a window in place. Everything has tooltips.
Disclaimer
5etools is intended as an easily-accessible digital reference for products you already own. Please ensure you only access content in accordance with your local laws.