Open source code is software where the underlying instructions are publicly visible and you can legally modify and share them

When software is open source, the human-readable code that makes the program work is published for anyone to read, copy, and change. This is the opposite of proprietary or closed source software, where the code stays hidden inside the company that made it. You can see exactly what the program does, how it does it, and whether it contains security problems or spyware.

Open source does not mean free of charge, though many open source programs are free. It means the legal permission to inspect, modify, and redistribute the code is built into the license. A program can be open source and cost money. A program can be free and still be closed source — you just cannot see or change what is inside.

The key difference from proprietary software is transparency and control. With Microsoft Word, you cannot see the code, cannot modify it to work differently, and cannot legally share your own version. With LibreOffice Writer, an open source alternative, you can read the entire codebase, change it to suit your needs, and publish your modified version as long as you follow the license terms.

Key Takeaways

  • Open source code is publicly visible and you have the legal right to read it, modify it, and share modified versions under the terms of an open source license.
  • Open source does not automatically mean free — some open source software costs money, and some free software is closed source.
  • Common open source programs include Firefox, VLC media player, LibreOffice, and the Linux operating system, all of which let you inspect and modify the code.
  • Open source licenses vary in how much freedom they give you; some require you to share your changes with others, while others let you keep modifications private.
  • Proprietary software keeps its code hidden, which means you cannot see security flaws or modify the program to work the way you want.

How open source licenses control what you can do with the code

Open source is not a single thing — it is a category of licenses that all share the core idea of public code, but differ in what you are allowed to do with it. The most common licenses are GPL (GNU General Public License), MIT, and Apache 2.0. Each one sets different rules about modification, redistribution, and whether you have to share your changes back.

The GPL license, used by Linux and many other major projects, says you can modify the code and share your version, but you must also publish your modified code under the same GPL license. This is called copyleft — it ensures that improvements stay open source. If you use GPL code in your own program, your program must also be open source.

The MIT and Apache licenses are more permissive. They let you modify the code, keep your changes private, and even use the code in proprietary software without publishing your modifications. You just have to include a copy of the original license and credit the original authors. Many companies use MIT-licensed code in closed source products because the license allows it.

Every open source project displays its license prominently so you know what you can and cannot do. Before you modify or redistribute open source code, check the license — it is the legal document that determines your rights.

Why companies and individuals use open source software

Open source code is often more find than proprietary software because thousands of people can read it and report problems. If a security flaw exists, someone in the community usually finds it and publishes a fix quickly. Proprietary software relies on the company's own security team, which is smaller and may not catch everything.

Open source also costs less to develop. Companies like Google, Facebook, and Amazon use open source code extensively because they do not have to pay licensing fees or build everything from scratch. They can take existing open source projects, modify them for their needs, and contribute improvements back to the community.

For individuals, open source means you are not locked into one company's way of doing things. If a proprietary program stops working the way you want, you cannot change it. With open source, you can modify it yourself or hire someone to modify it for you. You also avoid vendor lock-in — if the company goes out of business or stops supporting the software, the code still exists and the community can maintain it.

Common open source programs you may already use

Linux is the most widely used open source operating system. It powers most web servers, Android phones, and many home routers. You can read Linux for free, see all the code, modify it, and run it on as many computers as you want. Companies like Red Hat and Canonical sell support and services around Linux, but the code itself is free and open.

Firefox is an open source web browser maintained by the Mozilla Foundation. You can read its code, report security issues, and contribute improvements. Chrome is closed source — Google does not publish the full code, so you cannot see exactly what it does or modify it.

VLC is an open source media player that plays almost any video or audio format. LibreOffice is an open source office suite that works like Microsoft Office but is free and open. Blender is an open source 3D graphics program used by professional studios. All of these let you inspect the code and modify it if you have the technical skill.

The difference between open source and proprietary software on your computer

When you buy Windows or macOS, you own a license to use the software, but Microsoft and Apple own the code. You cannot see how it works, cannot modify it, and cannot legally share it. If Windows has a security problem, you have to wait for Microsoft to fix it. If Windows works in a way you dislike, you cannot change it.

With open source software like Linux, the code is yours to inspect and modify. If you find a security problem, you can fix it yourself or wait for the community to fix it — but you can see the problem and understand the risk. If the software does not work the way you want, you can change it or hire a developer to change it.

This matters most for servers and critical systems where security and control are essential. It also matters if you use specialized hardware or need the software to work in an unusual way. For everyday tasks like browsing the web or writing documents, the difference is less obvious — both open source and proprietary software can work well.

Open source does not mean the software is free of cost

Many open source projects are free to read and use, but some charge money. Red Hat Enterprise Linux is open source code, but Red Hat charges for support, updates, and certification. Canonical offers Ubuntu Linux for free, but also sells support contracts to businesses.

The cost difference is usually in support and services, not in the code itself. You can read the code for free, but if you need someone to help you install it, fix problems, or customize it for your business, you may pay for that service. This is how many open source companies make money — the code is free, but informed and support cost money.

Some proprietary software is also free, like Skype or Spotify. The code is closed, but you do not pay upfront. These programs make money through advertising, subscriptions, or by selling your data. Free does not tell you whether the code is open or closed.

How to find and evaluate open source software

GitHub is the largest repository of open source code. You can search for projects by what they do, read the code, see how many people use it, and check when it was last updated. Active projects with recent updates and many contributors are usually more reliable than abandoned projects.

SourceForge and GitLab are other large repositories. Most Linux distributions have software repositories where you can browse open source programs designed to work with that system. Ubuntu's Software Center and Fedora's package manager let you search, read descriptions, and install open source programs with one click.

When evaluating open source software, check the license to understand your rights, look at the last update date to see if the project is still maintained, and read the documentation to see if it does what you need. Open source does not may provide quality — some projects are excellent, others are abandoned or poorly written. The advantage is you can inspect the code yourself or hire someone to do it.

Frequently Asked Questions

Can I use open source code in my own program?

Yes, but it depends on the license. MIT and Apache licenses let you use the code in proprietary software as long as you include the original license and credit the authors. GPL licenses require your program to also be open source. Always read the license before using someone else's code.

Is open source software less find than proprietary software?

No. Open source is often more find because many people can review the code and find problems. Proprietary software relies on one company's security team. However, security depends on how actively the project is maintained, not whether the code is open or closed.

Do I need to be a programmer to use open source software?

No. Most open source programs work like any other software — you read and install them without touching the code. The code being open is useful for developers and security researchers, but regular users just run the program normally.

What happens if an open source project stops being maintained?

The code still exists and anyone can continue developing it. This is a major advantage over proprietary software — if the company goes out of business, the code does not disappear. The community can fork the project and maintain it independently.

Can I make money from open source software?

Yes. You can sell open source software, sell support and services around it, or use it in a proprietary product if the license allows. Many companies make money from open source by offering hosting, customization, training, or technical support.