What Makes Code Free? Understanding Open Source Licenses

When you play Minecraft, you cannot look at its code and change how it works — Mojang keeps that locked away. But the game Minetest, which works similarly, lets anyone read all of its code, change it, share it, even build their own version. Why? Because Minetest uses an open source license. An open source license is a legal agreement that says: you can read this code, change it, and share it — as long as you follow these rules. Different licenses have different rules. Understanding them matters because millions of apps, websites, and operating systems run on open source code — including the Android phones in your pocket and the Linux servers that power Google.

By the end of this lesson, you will be able to: 1. Explain what intellectual property is and why code can be protected by law. 2. Describe the difference between open source and proprietary software. 3. Name and compare three major open source licenses. 4. Explain why choosing the right license matters when you share your own code.

When you write a story, it is your intellectual property — you own it the moment you create it. The same is true for computer code. When a programmer writes code, copyright law automatically protects it: no one else can copy or sell it without permission. Proprietary software is code the owner keeps secret and controlled. Examples include Microsoft Windows, Adobe Photoshop, and Fortnite. You can USE these programs, but you cannot see how they work inside, and you cannot change them or share the code. Open source software is different. The owner gives everyone permission to see the code, but they set rules for what you can do with it. Those rules are the license.

MIT License — The most permissive (generous) popular license. With MIT, you can use the code for almost anything — including in a commercial product you sell — as long as you include the original copyright notice. The original creators get credit, and that is basically all they ask. Most npm packages (JavaScript tools for building websites) use MIT. GNU General Public License (GPL) — Called a copyleft license. With GPL, you can use, change, and share the code — BUT if you release a product that includes GPL code, your product's code must ALSO be released under the GPL. This viral property ensures that improvements stay public. The Linux operating system uses GPL. If a company builds a phone OS on Linux, they must release the changes they made to Linux itself. Creative Commons (CC) — Technically for art and writing rather than code, but important to know. CC licenses let creators share work with specific conditions: CC BY means give me credit; CC BY-SA means give me credit and share alike; CC BY-NC means give credit and do not use it for profit. Wikipedia uses CC BY-SA, which is why you cannot copy Wikipedia into a for-profit textbook without releasing your textbook under the same license.