GNU Lesser General Public License (LGPL)

When releasing open-source software, choosing the right license is crucial. You want to protect your code, support collaboration, but also allow others to use it freely—including in commercial or proprietary applications. This is exactly the goal of the GNU Lesser General Public License (LGPL).

LGPL offers a middle ground between the stricter GPL license and more permissive ones like MIT or Apache 2.0. It’s especially useful for open-source libraries that are meant to be used in closed-source software without forcing the entire application to be open.

In this article, we’ll cover:
✅ What the LGPL license is and how it works
✅ Differences between LGPL and GPL, MIT, Apache
✅ When to use LGPL and real-world examples
✅ Clear comparison table for easier understanding

Let’s dive into this uniquely balanced license! 🚀

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1. What is the LGPL License? 🔍

The GNU Lesser General Public License (LGPL) is a free software license developed by the Free Software Foundation (FSF).

Originally known as the “Library GPL“, it was created to license software libraries in a way that allows them to be used by both open and closed-source applications.

🔑 Key Features of LGPL:

• Copyleft applies only to the library code, not to the application that uses it.
• Modifications to the LGPL-covered code must be released under the same license.
• You can dynamically or statically link the library without needing to open-source your entire app—provided you allow reverse engineering or re-linking with a modified version of the library.

📌 In simple terms: You can use LGPL libraries in proprietary software, but if you modify the LGPL library itself, you must publish those changes.

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2. LGPL vs. GPL: What’s the Difference? ⚖️

Aspect	GPL (General Public License)	LGPL (Lesser General Public License)
Copyleft strength	Strong: affects all code linked to GPL software	Weak: affects only the library itself
Use in proprietary software	❌ Not allowed unless the whole project becomes GPL	✅ Allowed, as long as LGPL conditions are respected
Modifying the library	Must release entire source code under GPL	Must release only library modifications under LGPL
Best use case	Standalone open source apps (OS, editors, etc.)	Reusable libraries (graphics, audio, data processing)
Popular projects	Linux kernel, GCC, WordPress	FFmpeg (LGPL variant), Glib, SDL, libpng

📌 Copyleft Reminder: LGPL lets proprietary programs link to the library without inheriting its license.

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3. LGPL vs MIT vs Apache vs BSD: License Comparison Table 📊

License	Copyleft	Allows Proprietary Use	Requires Disclosing Source	Patent Protection	Best For
GPL	✅ Strong	❌ No	✅ Yes (entire app)	❌ No	Fully open-source applications
LGPL	✅ Weak	✅ Yes	✅ Yes (library only)	❌ No	Shared libraries and SDKs
MIT	❌ No	✅ Yes	❌ No	❌ No	Maximal compatibility and reuse
Apache 2.0	❌ No	✅ Yes	❌ No	✅ Yes	Corporate use, cloud/AI libraries
BSD (2/3-clause)	❌ No	✅ Yes	❌ No	❌ No	Academic/research-friendly projects

📌 Summary: LGPL balances openness with practical use in both open and closed software ecosystems.

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4. When Should You Use the LGPL? 🤔

✅ Use LGPL if:

• You’re building a reusable library or SDK and want it adopted widely, including by proprietary software.
• You want modifications to your library to be shared, but not impose rules on entire programs using it.
• You want to promote open-source development while enabling industry adoption.

❌ Avoid LGPL if:

• You want all derivative software to remain 100% open source (use GPL instead).
• You want maximum licensing flexibility with no redistribution requirements (consider MIT or Apache).
• Your code is not a library but a full application or platform (GPL might be more appropriate).

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5. Real-World Examples of LGPL Projects 🌍

Many major software libraries use LGPL to maximize adoption without compromising core freedoms:

• 🖼 libpng – image processing library used in web browsers & games
• 🎥 FFmpeg (LGPL variant) – used for video encoding/decoding in VLC, YouTube, and OBS
• 📊 Gnuplot – powerful graphing utility used in science and engineering
• 🖥 SDL (Simple DirectMedia Layer) – game development and multimedia input/output
• 🧠 Glib – core library for the GNOME desktop environment

📌 These libraries are often embedded into both open-source and proprietary applications worldwide.

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6. Developer Obligations Under LGPL 📎

If you distribute a binary application that uses an LGPL library, you must:

1. Provide access to the LGPL library’s source code, including your modifications.
2. Allow users to relink your app with a modified version of the LGPL library.
3. Include a license notice and disclaimer.

📌 Note: If you dynamically link, compliance is easier. Static linking may require distributing object files to enable relinking.

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Conclusion 🧠🔓

The LGPL license is an excellent option when you want to create open and reusable libraries without placing too many restrictions on the people who use them—even in commercial or closed-source applications.

By combining copyleft protection for the core code and flexibility for end users, LGPL helps drive both freedom and adoption. It’s a favorite for developers building foundational software, especially where broad compatibility is key.

🌟 In a world where openness and collaboration matter—but so does flexibility—LGPL hits the perfect balance. 🌟

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📌 Key Takeaways:
✅ LGPL applies copyleft only to the library, not the entire app.
✅ It allows proprietary software to use open libraries under clear conditions.
✅ You must disclose changes to the library, but not to the entire codebase.
✅ It’s ideal for SDKs, shared tools, and open-source libraries.
✅ LGPL sits between GPL’s strictness and MIT/Apache’s permissiveness.