Primer is GitHub’s internal CSS toolkit. It’s been the base coat for GitHub.com for years now, providing styles for our global typography, layout, tooltips, buttons, and more. Starting today, it’s open source.

Primer isn’t another large front-end framework, though. It’s rather limited in functionality and isn’t intended to replace something like Bootstrap. It will always be GitHub’s internal toolkit first, designed to help build GitHubby things. That said, we love to share.

Primer is licensed MIT, so you can basically do whatever you like with the source code. We’ll be a little stringent on merging new features to the project for the foreseeable future though. Longer term, we envision having a suite of Primer projects—one repository for each new component. More on that another time though.

For now, head to GitHub to view the source code and read through the docs at http://primercss.io.