In yesterday’s tip, you saw how to select a license when you create a new project. Today’s tip is about how to get that license picker back for an existing repo.

Since licensing is done based on the content of a file named license in your repo, instead of metadata about the GitHub repository that lives alongside the repo, first, you’ll want to create a new file in your repo.

Next, type in License and over to the right, the license dropdown button (re)appears. You can call the file license, license.md, LICENSE, or LICENSE.MD, as long as the filename is “license”

When you select a license, for example the MIT License,

and you’ll see that the license text is inserted and some boilerplate information, like copyright year and name, are inserted.

Now when you commit this file (and wait a minute or so), you’ll see that GitHub now displays the license name at the top of the repo.

Suppose you didn’t choose a license via the dropdown picker (either on /new or in the method described above). Suppose you’ve previously pushed a license file up to GitHub at some prior point.

GitHub uses an open source project called Licensee to do license detection, i.e. compare the license file to the list of licenses coming from the Choose a License website. According to the GitHub blog, “Licensee is the same code we use to provide the Licenses API and understand how repositories on GitHub are licensed.”

If you want to contribute to licensee, there’s a contributing guide in the repo. If you’re looking to add a new license that can be detected, you’ll want to check out the choose a license repo.

• Git(Hub) Tip of the Day 2017