Understanding Open Source Licenses in Game Development

Why Licenses Matter for Game Developers

Every open source game you find in our games directory is governed by a license. This license determines what you can and cannot do with the code. Understanding licenses is essential whether you are using open source games for learning, contributing to projects, or building your own games with open source components.

Choosing the wrong license can create legal complications. Using code without following license terms can result in lawsuits or forced open-sourcing of your work. This guide explains the most common licenses and helps you navigate the open source licensing landscape.

The Main License Categories

Permissive Licenses

Permissive licenses grant maximum freedom to users. You can use, modify, and distribute code with minimal restrictions. The main requirement is typically including the original license and copyright notice.

Examples: MIT, BSD, Apache 2.0, zlib

Permissive licenses are popular for game development because they allow commercial use without source disclosure requirements. Many game engines use permissive licenses for this reason.

Copyleft Licenses

Copyleft licenses require that derivative works use the same license. If you modify and distribute copyleft code, you must also distribute your modifications under the same terms.

Examples: GPL, LGPL, AGPL

Copyleft licenses ensure that improvements remain open source. They are common in Linux games and community-driven projects.

Public Domain

Some developers release their work into the public domain, waiving all rights. You can do anything with public domain code without restrictions.

Examples: CC0, Unlicense, WTFPL

Public domain dedications provide maximum freedom but may have legal complications in some jurisdictions.

Common Licenses Explained

MIT License

The MIT License is the most popular open source license. It requires only that you include the copyright notice and license text in copies of the software.

You can:

• Use the code commercially

• Modify the code

• Distribute the code

• Use the code in proprietary projects

You must:

• Include the original license and copyright notice

Example games: Many JavaScript games and Phaser projects use MIT.

GNU General Public License (GPL)

The GPL is the most common copyleft license. It requires that derivative works also be released under the GPL. This "viral" nature ensures that GPL code remains open source.

Version differences:

• GPL v2: Original version, still widely used

• GPL v3: Adds patent protections and anti-tivoization clauses

You can:

• Use the code commercially

• Modify the code

• Distribute the code

You must:

• Distribute source code with binaries

• Use GPL for derivative works

• Include the original license

Example games: 0 A.D., many classic open source games.

GNU Lesser GPL (LGPL)

The LGPL is a compromise between MIT and GPL. It allows linking LGPL libraries with proprietary code, provided the library itself remains LGPL. This is common for game libraries and engines.

You can:

• Link LGPL code with proprietary code

• Use the code commercially

You must:

• Keep LGPL portions under LGPL

• Allow users to replace the LGPL components

Example uses: SDL, many game development libraries.

Apache License 2.0

The Apache License is permissive like MIT but includes explicit patent grants. Contributors automatically license any patents needed to use their contributions.

You can:

• Use the code commercially

• Modify the code

• Use the code in proprietary projects

You must:

• Include the original license

• State changes made to the code

• Include NOTICE file if present

Example uses: Many Bevy engine projects, enterprise game tools.

Creative Commons Licenses

Creative Commons licenses are designed for creative works rather than code. They are commonly used for game assets like art, music, and documentation.

CC0: Public domain dedication, no restrictions CC BY: Attribution required CC BY-SA: Attribution and share-alike required CC BY-NC: Attribution, non-commercial use only

Many open source games use different licenses for code (MIT/GPL) and assets (CC licenses).

Practical Licensing Scenarios

Using Open Source in Your Commercial Game

If you want to use open source code in a commercial game:

• Permissive licenses (MIT, BSD, Apache): You can include the code with proper attribution. Keep a LICENSES file listing all open source components.

• LGPL libraries: You can link dynamically. Users must be able to replace the library. Include the LGPL license text.

• GPL code: You must release your entire game under GPL or avoid using the code entirely. Consider alternatives if you want a proprietary game.

Contributing to Open Source Games

When contributing to existing projects, your contributions typically fall under the project's existing license. Some projects use Contributor License Agreements (CLAs) that grant additional rights to the project maintainers.

Before contributing, check:

• The project's LICENSE file

• The CONTRIBUTING.md file for CLA requirements

• Whether you can assign your copyright or grant sufficient rights

Choosing a License for Your Game

For your own open source game, consider your goals:

Maximum adoption: Use MIT or Apache 2.0. These permissive licenses encourage both commercial and open source use.

Ensuring derivatives remain open: Use GPL v3. This copyleft license prevents proprietary forks.

Engine/library use: Consider LGPL. This allows commercial games to use your code while keeping improvements open.

Asset freedom: Use CC0 for art and audio if you want unrestricted use.

License Compatibility

Not all licenses work together. When combining code from multiple sources, you must ensure licenses are compatible.

Compatible Combinations

• MIT + MIT = MIT

• MIT + Apache 2.0 = Apache 2.0

• MIT + GPL = GPL (the result must be GPL)

• LGPL libraries + proprietary code = works if properly linked

Incompatible Combinations

• GPL v2 only + Apache 2.0 = incompatible (GPL v3 resolved this)

• GPL + proprietary = incompatible

• Different copyleft licenses may conflict

Always verify compatibility before mixing licensed code. The SPDX license list provides official compatibility information.

Compliance Best Practices

Maintain a LICENSE File

Include a LICENSE file in your project's root directory containing your chosen license text. For multi-license projects, use a LICENSES directory with individual license files.

Track Dependencies

Maintain a list of all third-party dependencies and their licenses. Many build tools can generate this automatically. Include this information in your distribution.

Document Asset Licenses

Game assets often have different licenses than code. Create an ATTRIBUTION file listing all assets, their sources, authors, and licenses.

Follow Notice Requirements

Some licenses require including NOTICE files or preserving copyright headers. Ensure your build process does not strip required notices from distributed files.

Common Misconceptions

"If it's on GitHub, it's free to use"

False. Code without a license defaults to "all rights reserved." You cannot legally use it without permission. Always check for a LICENSE file.

"Personal projects don't need licenses"

While you control your personal projects, adding a license clarifies permissions for others. If you want contributions, you need a license.

"The GPL means I can't sell my game"

False. You can sell GPL software. You must provide source code to purchasers, but you can still charge for your work.

"MIT code becomes my property"

False. MIT grants a license, not ownership transfer. The original authors retain copyright. You can use their code under the license terms.

Resources for Further Learning

Explore licensed projects in our games directory. Each game listing shows its license, helping you understand what is allowed.

For more information:

• Choose A License: Simple license selection tool

• SPDX License List: Official license identifiers

• tl;drLegal: Plain-language license explanations

Conclusion

Understanding open source licenses empowers you to use, contribute to, and create open source games confidently. Whether you are building with MIT-licensed libraries, contributing to GPL projects, or choosing a license for your own game, this knowledge is essential.

Browse our games directory with your new understanding of licenses. Check the license before using any code, and choose the right license for your own projects. With proper licensing knowledge, you can participate fully in the open source gaming community.