DEV Community

Piotr S
Piotr S

Posted on

Open Source Licensing: What Mid-Level Developers Must Know to Avoid Legal Trouble

As developers, we live on open source. npm install, pip install, go get… we build on the work of others. It’s amazing, fast, and collaborative. We see a project on GitHub, see the “MIT” license, and think, “great, it’s free!”

But “free” does not mean “no rules.” And as a mid-level developer, you’re past the “junior” stage of just making it work. You’re now expected to build things that are safe—both for security and for the law.

Misunderstanding the difference between an MIT license and a GPL license is a rookie mistake that can—and this is not an exaggeration—destroy your company’s product or land it in a massive lawsuit.

When a recruitment agency get-talent.eu in Europe is vetting you for senior jobs in the EU, they’re not just testing your coding skills; they’re testing your professional maturity. This is a big part of it.

📜 The Two “Families” of OSS Licenses

You don’t need to be a lawyer, but you do need to know the two main categories.

  1. Permissive Licenses (The “Do Almost Anything” Bunch) These are a developer’s best friend.
  • Examples: MIT, Apache 2.0, BSD.
  • What they mean: You can use the code in your own projects, even if your project is proprietary, closed-source, and makes your company millions.
  • Your Only Obligation:You just have to include the original copyright and license text somewhere in your application’s documentation (that “Acknowledgments” screen in your app? That’s what it’s for).

2. Copyleft Licenses (The “Share-Alike” Bunch)

This is where the danger lies. These licenses are built on a philosophy: “If you use our free code, your code must be free, too.”

  • Examples: GPL (v2, v3), AGPL.
  • What they mean: If you use a GPL-licensed library in your application, your entire application is now considered a “derivative work.”
  • The Consequence: You are now legally obligated to make your entire application’s source code publicly available under the same GPL license.

The “Viral” License: Why Your Company’s Lawyers Fear the GPL

The term for this is “viral.” The GPL “infects” any code it touches.

Let’s paint a picture:

  1. You’re building your company’s new proprietary, million-dollar algorithm.
  2. You find a small command-line-parser library on GitHub that’s perfect. It’s licensed under GPLv3.
  3. You use it. You ship the product.
  4. A competitor finds out. They sue.
  5. The Result: A court can force your company to either A) stop selling its product entirely or B) release the entire source code for its million-dollar algorithm to the public, for free.

This is a company-killing mistake.

The Even Scarier One: AGPL

There’s one more you must know: AGPL (Affero General Public License).

  • Used by: MongoDB (in the past), Grafana, and many other popular “open core” tools.
  • What it means: It’s the GPL, but it also triggers “over a network.”
  • If you just run an AGPL program on a server and let users interact with it (like a SaaS product), you must make your (potentially modified) source code available to all users.
  • The Rule: If you don’t modify the AGPL code and just use it (e.g., your app just talks to a standard MongoDB database), you are generally fine. If you modify the AGPL code itself, you’re in the danger zone.

Your New Workflow: “Stop and Check”

As a mid-level dev, you’re the gatekeeper.

  1. Check Before You Install: Before you npm install anything, spend 5 seconds. Go to the GitHub repo. Look at the LICENSE file.
  2. Know Your Company’s Policy: Every mature tech company has an “approved” list. It’s almost always MIT, Apache, BSD. Anything else, especially GPL or AGPL, must be “ask-legal-first.”
  3. Use Tooling: You don’t have to do this manually. Your CI/CD pipeline should be running license-checking tools (like Snyk, FOSSA, or WhiteSource). These tools scan all your dependencies and report on their licenses, flagging any “high-risk” ones before you merge to main.

Conclusion

This isn’t meant to scare you away from open source. OSS is fantastic. This is about being a professional. A carpenter knows the difference between a nail and a screw. A professional developer knows the difference between MIT and GPL.

Understanding this risk is a key part of your developer career progression. It’s what makes you a trusted engineer, not just a coder.

For more information, please refer to our blog

Top comments (0)