What Is Open Source License? A Practical Guide

At its heart, an open source license is a legal document that sets the ground rules for how you can use, change, and share software that’s been made publicly available. Think of it as the ‘terms of service’ for free code, giving you permissions that standard copyright law would normally hold back.

Unpacking the Idea of an Open Source License

Imagine software is like a recipe for a cake. With proprietary or “closed source” software, all you get is the finished cake. You can eat it, but you have no idea what the ingredients are or how it was made.

An open source project, on the other hand, hands you the entire recipe card—the source code. But just because you can see the recipe doesn’t mean you can do anything you want with it.

That’s where the open source license steps in. It’s the “rulebook” attached to that recipe. It tells you exactly what you’re allowed to do. Can you bake the cake for yourself? Sure. Can you tweak the amount of sugar? Probably. Can you sell your modified version at a bake sale? Now, that depends entirely on the license.

The Foundation of Open Source

For a license to be officially considered “open source,” it needs to meet a specific set of criteria laid out by the Open Source Initiative (OSI). These principles are designed to make sure the software genuinely encourages collaboration and sharing. This image from the OSI website shows the ten core principles that every true open source license must follow.

These rules guarantee fundamental freedoms, like the right to redistribute the software and have access to its source code. They form the legal bedrock of the entire open source movement. And its adoption is staggering—the 2024 State of Open Source Report found that 95% of organizations increased or maintained their use of open source software over the past year. It’s not a niche concept anymore; it’s a core part of how modern technology is built.

At its core, an open source license is an instrument of freedom. It legally protects the rights of users and developers to see, study, change, and distribute software, fostering a global community of collaborative innovation.

This framework is what prevents a single company from swooping in and locking down community-driven code. The whole point is to ensure that what starts open, stays open for everyone to build upon.

This table gives a quick rundown of the essential rights that almost every open source license grants. These form a universal baseline of permissions you can pretty much always count on.

Core Permissions of an Open Source License

While these three permissions are the foundation, the real differences between licenses show up in the specific conditions and limitations they add on top of these rights. We’ll get into that next.

The Two Big Ideas: Permissive vs. Copyleft

When you start digging into open-source licenses, it can feel like you’re learning a new language. But here’s the good news: almost every license you’ll encounter falls into one of two main camps: permissive or copyleft.

Think of it as two different approaches to sharing. The permissive camp says, “Here’s my code. Go do what you want with it.” The copyleft camp says, “You can use my code, but whatever you build with it has to be shared under the same rules.” This one distinction is the key to everything, and it shapes not just a single project, but the entire community that forms around it.

Permissive Licenses: The Ultimate Freedom

Permissive licenses are all about encouraging the widest possible use of the code with the fewest strings attached. They’re incredibly straightforward and place very few restrictions on what you can do.

Really, their main requirement boils down to one thing: attribution. If you use code with a permissive license, you just need to give credit where it’s due by including the original copyright notice. That’s it. You can take the code, change it, and even bake it into your own closed-source commercial product without having to share your new source code.

Some of the most popular permissive licenses you’ll see are:

• The MIT License: This one is famous for being short and sweet. It basically says, “do whatever you want, just keep my name on it.”
• The Apache License 2.0: A bit more detailed than MIT, it explicitly grants patent rights from contributors, which makes it a popular choice for larger corporate projects.
• BSD Licenses: A family of simple licenses that, much like MIT, put the user’s freedom first.

Because they are so flexible, permissive licenses are a fantastic choice for libraries and tools. The creators want their code to be used everywhere, by everyone, and these licenses make that happen.

Copyleft Licenses: Protecting the Commons

Copyleft licenses operate on a completely different philosophy: “share-alike.” The main goal here isn’t just to give the code away, but to ensure that the code and anything created from it remains open and free for everyone, forever.

The core rule of copyleft is this: if you modify and distribute software under a copyleft license, you are required to release your changes under the exact same license. This is often called a “reciprocal” or even “viral” effect. It’s designed to stop someone from taking a community-built project, adding their own secret sauce, and then selling it as a closed-source product.

A copyleft license uses copyright law to ensure that every person who receives a copy or derived version of a work can use, modify, and also redistribute both the work and its derivatives. It’s a mechanism for keeping software free.

This is the principle that underpins massive projects like the Linux kernel and WordPress. The most famous copyleft license by far is the GNU General Public License (GPL). To get a better sense of which licenses are most popular, the Open Source Initiative provides a great breakdown.

Permissive vs. Copyleft: A Side-by-Side Comparison

Choosing between these two models is a major decision for any project. To make it clearer, let’s break down the key differences.

Ultimately, this table shows two valid but very different ways to foster an open-source community. Neither is inherently “better”—it all depends on the project’s goals.

The data clearly shows a trend: while permissive licenses are more widely used, copyleft licenses are the backbone of some of the most important open-source projects in the world. This balance between flexibility and protected freedom is what keeps the entire ecosystem healthy.

For mobile developers, understanding these licenses isn’t just a legal chore; it’s a crucial part of building a clean and efficient development pipeline. In fact, if you’re interested in how these concepts play out in real-world workflows, you might find our deep dive into Android continuous integration helpful.

A Look at the Most Common Open Source Licenses

Now that we’ve covered the big-picture philosophies—permissive vs. copyleft—let’s get our hands dirty and look at the actual licenses you’ll bump into in the wild. This is where the theory hits the road, translating high-minded ideals into the legal text that dictates how we all build and share software.

Every license has its own personality, a reflection of the project’s goals and the community’s values. We’ll walk through the big four: MIT, Apache 2.0, the GNU General Public License (GPL), and the BSD family. Getting a feel for their specific terms is the only way to really know what you can and can’t do with a piece of code.

The MIT License: The Minimalist

If a license were a handshake deal, it would be the MIT License. It’s the champion of simplicity—incredibly short, written in plain English, and one of the most popular permissive licenses out there for a reason.

Its core principle is freedom, granting you almost unlimited rein to do what you want with the software. You can use it, copy it, tweak it, and ship it, whether for free or as part of your own commercial, closed-source product.

So what’s the catch? There’s only one rule:

• You must include the original copyright and license notice in any version of the software you pass along. That’s it.

This “do whatever you want, just give me credit” attitude makes it a huge favorite for foundational libraries and frameworks, especially in the JavaScript ecosystem. Think of giants like React, Node.js, and jQuery—they all use MIT because their goal is to get into the hands of as many developers as possible with zero friction.

The Apache License 2.0: The Corporate-Friendly Choice

The Apache License 2.0 is another giant in the permissive world, but it comes dressed in a bit more of a business suit than the MIT license. It gives you the same broad freedoms to use, modify, and distribute code, but it adds a couple of important clauses that make legal departments breathe a little easier.

First, it includes an express grant of patent rights. In simple terms, this means that anyone who contributes code to an Apache-licensed project is also giving you a license to use any patents they hold that might cover their contribution. This is a huge deal, as it protects you from getting sued for patent infringement by a project’s own contributors down the line.

Second, it requires you to state any significant changes you’ve made to the original files. You still don’t have to release your source code, but this bit of transparency helps everyone keep track of how the software evolves. It’s these protections that have made Apache 2.0 the go-to for massive projects like Android, Kubernetes, and Swift.

The Apache 2.0 license hits a sweet spot. It maintains the open, collaborative spirit of a permissive license while adding the explicit legal protections that big companies need to manage risk.

The GNU General Public License (GPL): The Protector of Freedom

No discussion of open source is complete without the GNU General Public License (GPL). It’s the most famous and influential copyleft license, built with a single-minded mission: to guarantee that software remains free and open for every user, forever. It achieves this with the “share-alike” principle we talked about earlier.

If you use a chunk of GPL-licensed code in your project and then distribute that project, you are legally bound to release your entire project’s source code under the same GPL license. This is often called the “viral” effect, and it’s by design. It ensures the freedoms granted by the license are passed on to every future user.

Here’s a look at the kind of clear, rights-focused language you’ll find in the GPLv3 text itself.

This part of the license clearly defines what it means to “run the program,” hammering home the user’s freedom to use the software for absolutely any purpose. This powerful stance is what has allowed massive, community-owned ecosystems like Linux, WordPress, and Drupal to thrive. Don’t mistake the GPL for being anti-commercial—it’s not. It simply insists that any commercial use must also respect the end user’s freedom.

For mobile developers, understanding these rules is critical. Before you even think about how to publish on the App Store, you need to have your license compliance sorted out, as it can make or break your entire release strategy.

The BSD Licenses: The Classic Permissive Family

The BSD (Berkeley Software Distribution) licenses are a family of permissive licenses that have been around even longer than the MIT license. They share the same spirit: grant broad permissions and ask for very little in return.

You’ll mainly run into two versions today:

• 2-Clause BSD License: Often called the “Simplified BSD License,” it’s pretty much the same as the MIT license. Just keep the copyright notice intact.
• 3-Clause BSD License: This version tacks on one extra condition: you can’t use the names of the original project or its contributors to endorse or promote your own derivative work without getting their explicit permission first.

Both are highly respected and have been used to build foundational pieces of internet technology and operating systems. The choice between BSD and MIT often boils down to personal preference, as both are ultimately designed to get good code into as many hands as possible.

How to Choose the Right License for Your Code

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Picking an open source license isn’t just a legal box to check. It’s one of the most important strategic decisions you’ll make, setting the entire tone for your project’s future. It dictates who uses your code, how they use it, and what kind of community will form around it.

Get it wrong, and you can end up with some serious headaches. A license that’s too restrictive might scare away the very corporate users or contributors you want to attract. On the other hand, one that’s too permissive could let others package your hard work into proprietary products without ever giving anything back—which might be the exact opposite of what you intended.

The secret is to start with your goals. Figure out what you want to achieve with your code first, and that answer will almost always point you to the right license.

Start by Defining Your Project’s Goals

Before you get lost in the fine print of different licenses, take a step back. Think about the big picture and jot down your intentions for the project. These answers will be your compass.

Ask yourself a few simple questions:

• Who is this for? Are you building a tiny helper library for fellow developers? A framework for startups? Or a mission-critical platform for big enterprises?
• How should people use it? Are you cool with your code being used in commercial, closed-source software? Or is it absolutely essential that any new versions remain open for everyone?
• What kind of community do you envision? Do you want the widest possible adoption, no strings attached? Or are you trying to build a community that lives by the “share-alike” principle?

Your answers will quickly steer you toward one of the two main camps: permissive or copyleft. For example, if getting your code into as many projects as possible—including commercial ones—is your number one priority, a permissive license like MIT or Apache 2.0 is probably the way to go.

This screenshot from GitHub’s excellent resource, choosealicense.com, breaks down this thought process perfectly. It frames the decision around what you’re trying to accomplish.

The tool boils it down to your core motivation: Do you just want something simple and permissive? Are you worried about patents? Or do you need to make sure everyone who uses it shares their improvements back with the community?

Matching Goals to Specific Licenses

Once you have your goals clearly defined, matching them to a specific license becomes much easier. Let’s walk through a few common scenarios.

Scenario 1: You want maximum adoption and minimal friction. Your goal is simple: get your code used by as many people as possible. You don’t care if a massive corporation uses it in their secret, proprietary software. You just want it out there.

• Best Choice: The MIT License. It’s famously short, easy for anyone to understand, and places almost no restrictions on what people can do. It’s the path of least resistance.

Scenario 2: You’re concerned about patents or building for a corporate environment. You like the freedom of a permissive license, but you need to protect your project and its users from potential patent lawsuits.

• Best Choice: The Apache License 2.0. It’s another permissive license, but it includes an explicit clause that grants patent rights from contributors. This is a huge deal for many businesses and provides a layer of legal protection that MIT lacks.

Scenario 3: You believe deeply in the “share-alike” philosophy. Your main goal is to build a collaborative ecosystem. Anyone can use, change, and distribute your code, but they must share their modifications under the exact same open terms.

• Best Choice: The GNU General Public License (GPLv3). This is the gold standard for strong copyleft. It legally ensures that your project—and anything built with it—remains open source forever.

Choosing a license is the moment you declare your project’s values. It’s your statement on collaboration, commerce, and community. Make it a deliberate one.

While you’re thinking about open source, it’s helpful to see where it fits into broader software IP protection strategies. And if you’re building a mobile app, aligning your license choice with your team’s workflow is crucial. Our guide on agile mobile app development offers insights on how to sync your development process with your project’s overarching goals.

How to Use Open Source Software Safely

Tapping into open source is like inviting an army of brilliant collaborators to join your project. It’s an incredible advantage, but it’s not a free-for-all. Working with the open source community means playing by the rules—the legal and ethical frameworks that keep the whole ecosystem running.

Ignoring license terms can land you in serious trouble, from public embarrassment to a courtroom.

At the very least, you have to give credit where it’s due. Even the most relaxed licenses, like the MIT License, have a core requirement of attribution. It’s the golden rule of open source: if you use their work, you credit the creators.

This usually just means keeping the original copyright notice and a copy of the license text somewhere in your project. It’s a simple sign of respect that also happens to be a legal necessity.

Navigating License Compatibility

Things get tricky when you start mixing code from different projects. Think of your application as a recipe. Each open source library is an ingredient, and each ingredient comes with its own instructions. You can’t just toss everything together and hope it works. Some ingredients just don’t mix.

For instance, pulling a library licensed under the strong copyleft GPLv3 into your proprietary commercial app is a recipe for disaster. The GPL’s “share-alike” rule would legally obligate you to release your entire application’s source code. For most businesses, that’s a deal-breaker. This is exactly why license compatibility is so important.

A single problematic dependency, hidden deep in your project, could put your entire product at risk. You absolutely have to know what you’re using.

Open source compliance isn’t a one-time check. It’s a continuous part of your development lifecycle. Every time you add or update a dependency, you have to re-verify that you’re still meeting all the license requirements.

The only way to manage this is to keep a detailed inventory of every open source component in your project. And I don’t just mean the libraries you install directly. You also have to track their dependencies—the “transitive dependencies”—because they all have their own licenses, too.

Automating Compliance with Modern Tools

Trying to track hundreds of dependencies by hand is a nightmare waiting to happen. It’s just not practical. This is where Software Composition Analysis (SCA) tools save the day. SCA tools scan your codebase and automatically identify every open source piece and its license.

Here’s what these tools do for you:

• Dependency Discovery: They create a complete Bill of Materials (BOM), giving you a full list of every open source library in your app.
• License Detection: They pinpoint the license for each component and flag anything that’s unusual or missing a license.
• Policy Enforcement: You can create rules—like “no GPLv3 licenses allowed”—and the tool will automatically enforce them.
• Vulnerability Scanning: On top of license compliance, SCA tools also scan for known security flaws in the open source code you’re using.

An SCA tool turns compliance from a high-stakes guessing game into a methodical, predictable process. It gives you the clear view you need to use open source safely and responsibly.

Building these habits is a key part of any solid development pipeline. For a deeper dive, check out our guide on application security best practices, which covers how to build a secure workflow from the ground up. By pairing smart internal policies with the right automated tools, your team can build amazing things without ever running afoul of the community that makes it all possible.

Common Questions About Open Source Licenses

Diving into open source licenses can feel like wading into legal jargon, and it’s natural for questions to pop up. Even when you understand the big picture of permissive vs. copyleft, the real world throws curveballs. Let’s tackle some of the most common questions developers and businesses run into, with straightforward answers to clear the air.

My aim here is to cut through the legal fog so you can feel confident using, contributing to, and even publishing open source software.

Can I Use Open Source Software in Commercial Products?

Yes, absolutely. This is probably the biggest myth out there. In fact, the freedom to use software for commercial purposes is a cornerstone of what makes open source, well, open source. The real question isn’t if you can use it, but how.

It all comes down to the license attached to the code.

• Permissive licenses (MIT, Apache 2.0) are a commercial developer’s best friend. They have very few strings attached, usually just requiring you to keep the original copyright notice somewhere in your product. You can bake this code into your proprietary software and you’re not forced to share your own secret sauce.
• Copyleft licenses (GPL) also allow commercial use, but they come with a big condition. If you build a product that uses GPL code and you sell or distribute it, you have to release your entire product’s source code under the same GPL license. It’s the “share-alike” rule in action.

This is a critical distinction, and it’s why many companies stick to permissively licensed code for their core products.

What Happens If I Ignore an Open Source License?

Ignoring an open source license is more than just bad form—it’s copyright infringement, plain and simple. The license is a legal contract, and when you don’t follow its terms, you’re using the software without permission.

The fallout can vary. Sometimes, you might just get a polite email from a developer asking you to add the right attribution. For a business, though, the stakes are much higher. Non-compliance can trigger legal action, potentially forcing you to pull your product from the market, pay damages, or even release your proprietary code.

Ignoring a license is a breach of the legal agreement that grants you the right to use the code. Beyond legal risk, it damages your reputation within the developer community, which is built on trust and mutual respect.

Is Public Domain the Same as Open Source?

Nope, they’re two very different beasts. Code in the public domain is completely free of copyright. The original creator has waived all their rights, so anyone can use it for absolutely anything, no questions asked. Think of it as a park bench—it’s there for everyone, with no rules attached.

On the other hand, open source software is still protected by copyright. The license is the key; it’s a legal document that grants you specific permissions to use, modify, and share the code under a set of rules. It’s less like a park bench and more like a library book: you can use it, but you have to follow the library’s rules. This structure protects both the creator and the user.

Why Do I Need a License for My Code on GitHub?

If you push code to a public GitHub repository without a license, you create a legal mess. By default, your code is protected by exclusive copyright law. That means people can look at it and even fork it, but they have no legal right to actually use, change, or share it in their own projects.

This ambiguity is a huge red flag for other developers. No one wants to build on a foundation that might crumble under a legal challenge. By simply adding a LICENSE file, you’re telling the world exactly how they can use your work. It removes the guesswork and is the first real step to becoming a good citizen of the open source community. For developers in certain ecosystems, like Apple’s, understanding these rules is just as crucial as managing your credentials. You can learn more in our guide on the Apple Developer Certificate.

At CodePushGo, we’re big believers in the power of open source to spark innovation. Our platform is built on that spirit, giving you the tools to update your React Native apps instantly and securely. You can focus on shipping great features, not on waiting for app store approvals.