This is good advice. For example, here’s a tricky one: github.com/IanLunn/Hover/blob/master/license.txt

Hover.css is made available under a free personal/open source or paid commercial licenses depending on your requirements.

Would you need to pay Ian Lunn Design to incorporate the library into your portfolio website? It’s used for a commercial purpose technically, but you’re not selling the website to a client. This is a source-available free software license, rather than a free software license. A free software license permits you to use the software for anything, with the only obligations usually being around keeping copyright notices intact and licensing your code in a certain way.

Generally, free software licenses are simpler and you’ll usually be fine so long as you keep your code available under the same terms. Of course, things get a bit tricky when combining incompatible free software licenses…

Compatibility is important if you want to combine software with two different licenses into one major work.

Generally speaking, most software on Github tends to be licensed under a few free software licenses, which are interoperable with each other:

• MIT License
• GPL, LGPL, and AGPL Licenses, which have one major difference in obligations between them
• ISC License
• Apache 2.0 License
• Mozilla 2.0 Public License

However, when you combine MIT and GPL together, you may be obligated to distribute any changes you make to the MIT-licensed portion, depending on how strongly it’s associated with the GPL portion. This is because the GPL is copyleft—that is, it requires you to provide anyone you transmit the binary form of the software to the associated sources if they ask for them. The MIT license does not require this obligation.

None of this really matters for a website, though, because you’re not transmitting the software; you are instead providing a service. Do keep an eye out for the AGPL, because this one applies even with server-side software interacting with clients.

I think writefreesoftware does a good job of explaining licensing for developers in simpler terms than the GNU Project: writefreesoftware.org/learn/licenses/

Sorry for the length…it’s kind of a complex topic.