Bootstrap is released under the MIT license and is copyright 2021 Twitter. Boiled down to smaller chunks, it can be described with the following conditions.

It requires you to:

• Keep the license and copyright notice included in Bootstrap’s CSS and JavaScript files when you use them in your works

It permits you to:

• Freely download and use Bootstrap, in whole or in part, for personal, private, company internal, or commercial purposes
• Use Bootstrap in packages or distributions that you create
• Modify the source code
• Grant a sublicense to modify and distribute Bootstrap to third parties not included in the license

It forbids you to:

• Hold the authors and license owners liable for damages as Bootstrap is provided without warranty
• Hold the creators or copyright holders of Bootstrap liable
• Redistribute any piece of Bootstrap without proper attribution
• Use any marks owned by Twitter in any way that might state or imply that Twitter endorses your distribution
• Use any marks owned by Twitter in any way that might state or imply that you created the Twitter software in question

It does not require you to:

• Include the source of Bootstrap itself, or of any modifications you may have made to it, in any redistribution you may assemble that includes it
• Submit changes that you make to Bootstrap back to the Bootstrap project (though such feedback is encouraged)

The full Bootstrap license is located in the project repository for more information.