Open Source Licenses Explained

Open source licenses serve as a legal agreement between open source author and user: authors make OSS available for free, but with certain requirements the user must follow.

When it comes to long-term planning for your project, it’s useful to understand the open source software licenses available so that you can make an informed decision about which one best suits your project’s needs.

In this article, we will share information about rights you have when your work is created (such as copyright), and how licensing helps establish the legal agreement you want your users to abide by when using your software.

What is an Open Source License?

The simplest explanation is that an Open source license is a license for computer software and other products that allows the source code to be used, modified, or shared under defined terms and conditions.

Open Source does not mean the software is available to use, copy, modify, and distribute as desired. Depending on the type of open source license, you may be allowed to modify the source code to meet your needs or fix any issues.

The license will determine the freedom you have with the software and its source code.

Software licenses have different levels of restrictiveness

Types of Open Source Licenses

There are two main types of open source licenses: permissive and copyleft. Permissive licenses tend to have fewer restrictions on use of the licensed code than copyleft licenses.

Here’s a full breakdown.

Open-Source Licenses Categories

Copyleft? You Mean Copyright, Right?

Actually, copyleft does exist, and as you can guess it is the opposite of copyright. While copyright restricts the use and distribution of a work, copyleft licenses allow that as long as the terms stated are obeyed.

Imagine you wrote a cookbook and you have the copyright to the book. This means that only you have the exclusive right to use, sell, and distribute the book. No one else can sell or distribute copies of your book without your permission.

Now, imagine that you wrote an open-source cookbook and released it under a copyleft license. This means that anyone can use, modify, and distribute the book for free, as long as they also share their modifications and any derivative works under the same copyleft license.

In this case, the book becomes a collaborative effort, with everyone adding and improving the recipes. The goal of copyleft is to ensure that the book remains freely available and that future modifications are also freely available.

As explained in this example, copyright gives the creator control over their work, while copyleft encourages collaboration and sharing.

Copyleft licenses can be further divided into:

Strong copyleft licenses : If a source code is protected by a strong copyleft license, then the derivative software needs to be publicly available under the same license. This includes all linked libraries and components within the software.

For example, if someone modifies and distributes software under a GPL license, they must also make the source code available and license their modifications under the same GPL license.

Weak copyleft licenses : The requirements of a weak copyleft license are similar to those of a strong one, but they apply to a limited set of codes.

This open-source license only requires that the source code of the original or modified work is made publicly available, while the rest of the code used together with the work doesn’t have to be published under the same license.

Permissive Licenses

Permissive open-source licenses are a type of open-source license that allows for greater flexibility in the use and distribution of open-source software.

Permissive licenses, such as the MIT License and the BSD License, place minimal restrictions on the use, modification, and distribution of the software.

With permissive licenses, users are free to use the software for any purpose, including commercial purposes, and are not required to release the source code or license their modifications under the same terms.

This allows for greater flexibility in the use and distribution of the software, but can also lead to the creation of closed, proprietary derivative works.

Permissive licenses are often favored by businesses and individuals who want to use open-source software as a component in their own proprietary software, as they provide greater freedom to use the software in their own projects.

Popular Permissive Software Licenses

MIT License
BSD License
Apache License

Popular Copyleft Software Licenses

GNU General Public License (GPL)
Mozilla Public License
Eclipse Public License

SNYK has published an Open source licenses comparison table which is worth to have a quick look.

Open source licenses comparison: popular copyleft licenses and permissive open source licenses.

Applying an Open Source Software License

In the most common scenario, you will want to place a file named LICENSE at the root of your project sources. You are certainly allowed to use any appropriate file extension to identify the file’s markup — i.e. this could be LICENSE.md for markdown, .html for HTML, and so on.

Having said that, and considering that this file contains very specific legal verbiage, it is best to leave it be plain text and named just LICENSE without any extension.

But please, for all our sakes, please do indeed use all caps in the file name. Such is the convention, and conventions exist for a reason. Most of the time, anyway.

Adding an Open Source Software License to New Projects

Many modern SaaS tools such as GitHub and GitLab will allow you to choose the license when the repository is first created. This is, perhaps, the single simplest way you can ensure your projects contain the right legal protections from the start.

Once you start the “Create new repository” workflow, GitHub will present you with the following screen, which contains a relevant checkbox toward the bottom. Checking the box opens up the drop-down with numerous licensing options to choose from.

How to Choose the Best Open-Source License for Your Code?

So you are ready to share your latest software creation with the world, but unsure which open-source license to opt for? With so many licenses out there and almost all written in not so easily understandable ways, choosing the right one can be a tricky business.

Here are some ideas and aspects to consider to help you decide:

If you plan to contribute to a community, the easiest way is to choose the license used by the community.

Doing so the project you contribute to the community would fit in perfectly since not all licenses are compatible with one another. Also, some communities restrict the use to only particular licenses.

For example, WordPress is released under GPLv2 and that’s the only license you can use if you want to contribute to the WordPress community.
If you want to make your code as reusable and shareable as possible, to secure the reciprocity you should choose GNU GPLv3. This way others can do almost anything they want with the code apart from distributing closed-source versions.
If you want to make it easy and permissive, to let people do with your code whatever they want, including publishing the derived work as proprietary, you should opt for an MIT license.

Conclusion

Open-source licenses play a critical role in the development and distribution of open-source software. They provide a clear framework for the sharing and use of software, allowing for collaboration, innovation, and the creation of high-quality software that benefits the entire community.

There is a variety of open-source licenses to choose from, including:

Strong Copyleft licenses (i.e. GPL)
Weak Copyleft licenses (i.e. LGPL)
Permissive licenses (i.e. MIT, BSD)

It’s important to choose the right license for your project, considering your goals for the software and the potential risks involved.

Some risks associated with open-source software include the possibility of others creating closed, proprietary derivative works and the risk of license compatibility issues if the software is combined with other software under different licenses.

In summary, while open-source licenses come with some risks, they also provide numerous benefits and opportunities for collaboration, innovation, and the creation of high-quality software. It’s important to carefully consider the right license for your project to ensure that your goals for the software are met.