general public licence

What Is the GNU General Public License (GPL)?

The GNU General Public License (commonly referred to as the "GPL") is a prominent open-source software license. It requires that whenever code is used, modified, or distributed, the source code must remain open and be shared under the same license terms. The GPL is one of the most influential licenses in the open-source ecosystem.

An "open-source license" defines the conditions under which an author allows others to use and modify their code—like sharing a recipe and permitting improvements. The GPL mandates that any improved version of the "recipe" must also be made public and shared under identical rules. This reciprocal requirement ensures that the community continually benefits from ongoing enhancements.

What Are the Core Principles of the GPL?

At its core, the GPL embodies the concept of "copyleft," which can be thought of as "reciprocal copyright": when you use or modify code made open by others, any distribution of your changes must also be open, and you must retain original copyright notices and licensing text.

Key principles include:

• Source Code Disclosure: When distributing executable files, you must also provide access to the corresponding source code.
• License Continuity: Derivative works must continue to use the GPL.
• Retention of Notices: Original copyright and license statements must remain intact.
• No Warranty: Software is provided "as-is," with no guarantees from the authors.
• Patent Provisions (v3): Version 3 of the GPL introduces clearer patent protection measures.

The Linux kernel has long used GPL-2.0 (as of 2025), making it one of the most recognized examples of GPL adoption.

How Does the GPL Impact Web3 Development?

The GPL affects whether you can distribute software using open-source code in closed-source form, or if you must open your source code when distributing your project. In Web3, GPL obligations can be triggered for node clients, wallets, frontends, and smart contracts.

For example, if your dApp frontend integrates a GPL-licensed component and you distribute an executable version to users, you may be required to release your frontend’s source code and retain all original notices. This fosters transparency in collaboration but may restrict closed-source business models.

On-chain, open-source practices enhance auditability and security. Many teams choose to release critical code to build trust but carefully assess license compatibility with their product strategy.

How Does the GPL Apply to Smart Contracts?

Smart contracts are typically written in Solidity, with licensing indicated at the top of files via the SPDX-License-Identifier (e.g., "SPDX-License-Identifier: GPL-3.0-or-later"). The GPL's requirements for reciprocal licensing present several considerations for smart contracts:

First, Distribution: Compiling and deploying a contract on-chain is generally considered public distribution. If your contract includes or modifies GPL code, public deployment may require you to open-source your modifications. Determining whether this constitutes distribution depends on context—evaluate during the design phase.

Second, Linking and Derivation: Contract inheritance or library calls are often treated as creating derivative works. If you inherit from a GPL-licensed contract, your distributed contract must comply with the same license.

Third, Common Practice: Many teams choose more permissive licenses like MIT or Apache for core contracts to reduce downstream obligations. If using the GPL, provide full source code, copyright notices, and build instructions in your repository to facilitate auditability and reuse.

How Does the GPL Differ from MIT and Apache Licenses?

The primary distinction between GPL, MIT, and Apache licenses is the strength of their reciprocal requirements.

• MIT: Like sharing a recipe with attribution—very permissive, does not require derivatives to use the same license. Suitable for closed-source products or dual licensing.
• Apache-2.0: Similar to MIT but includes explicit patent grants and disclaimers—meeting enterprise needs.
• GPL: Enforces reciprocal licensing, ideal for projects seeking ongoing community sharing of improvements; more restrictive for closed-source distribution.

In summary: Choose GPL for maximum open collaboration and mandatory sharing of enhancements; choose MIT or Apache for greater flexibility between open and closed-source commercialization.

How Do You Comply with the GPL in Your Project?

Step 1: Place the LICENSE file (the full text of the GPL) in your repository’s root directory, and state licensing details in your README.

Step 2: Add an SPDX-License-Identifier header (e.g., "SPDX-License-Identifier: GPL-3.0-or-later") at the top of each source file so toolchains can identify the license.

Step 3: Preserve original authors' copyright and license statements; clearly mark your own changes with date, author, and a summary.

Step 4: Provide a way to obtain source code for any distributed executables—for example, publishing source code, build scripts, and dependency documentation to ensure reproducibility.

Step 5: Review third-party dependencies for license compatibility; if necessary, use LGPL (more suitable for libraries) instead.

Step 6: Conduct a compliance review before going live; seek legal advice if commercial use is involved to minimize risk.

What Are the Differences Between GPL Versions?

The main versions are v2 and v3:

• v2 (e.g., Linux kernel): The oldest and most established version; does not address modern patent issues or device locking.
• v3: Strengthens patent grants, adds anti-Tivoization clauses (preventing hardware from blocking modified versions) and DRM-related terms—better suited to modern distribution scenarios.

"Or later" vs. "Only": Selecting "GPL-3.0-or-later" lets you adopt future versions for more flexibility; "only" fixes the version for better compatibility management.

Additionally, LGPL is intended for libraries (allowing linking under more permissive conditions), while AGPL extends open-source obligations to software provided over a network—Web3 backend services and frontend interactions should pay close attention to AGPL triggers.

Can You Use the GPL for Commercial Purposes?

Yes—the GPL permits commercial use. However, when you distribute derivative works containing GPL code, you must open-source your code and retain all notices. Common enterprise strategies include:

• Dual Licensing: Open-sourcing core code under the GPL while offering a commercial license version to enterprise clients.
• Service Model: Monetizing through hosting, support, auditing, or integration services while keeping code compliant with open-source requirements (note AGPL's specific obligations for network use).
• Component Separation: Isolating components that must be shared from proprietary business logic; using LGPL or proprietary alternatives for libraries to minimize reciprocal obligations.

What Are Common Risks and Misconceptions About the GPL?

Frequent misconceptions include:

• "GPL cannot be used commercially"—False. Commercial use is allowed but triggers open-source obligations when distributing derivatives.
• "No need to comply if not distributing"—Incomplete. Whether deployment constitutes distribution depends on context; on-chain deployment or network provision may count as public release.
• "GPL can be freely mixed with MIT/Apache"—Use caution. Derivative relationships may require adopting GPL throughout; avoid mixing incompatible licenses.
• "Minor use avoids obligations"—The way you incorporate code (inheritance, static/dynamic linking) may still create derivative works; compliance review is necessary.

Risks involve infringement and compliance disputes, which can impact funding, listings, or partnerships. Projects handling funds or contract security should complete license design and source audits early on.

Recommendations and Summary for Choosing the GPL

If your goal is fostering community collaboration, ensuring improvements are contributed back, and maintaining auditability, the GPL is a robust choice. If you require more freedom for closed-source or dual licensing models, MIT or Apache offer greater flexibility. Ensure consistent and traceable licensing for smart contracts and frontends—include LICENSE files and SPDX headers in repositories and standardize source code distribution paths. Be mindful of version differences, dependency compatibility, and whether your scenario constitutes distribution or derivation. Always conduct compliance checks and seek legal advice before commercializing. With a clear licensing strategy, you can achieve reliable collaboration and regulatory compliance in the Web3 ecosystem.

FAQ

Can I use GPL-licensed code directly in commercial projects?

Yes—but you must also release your derivative code as open source. The GPL's “viral” design means that if you develop a product based on GPL code and sell it, you are required to publish your source code under the same license terms. This core requirement makes it incompatible with closed-source business models. If your business relies on keeping code private, consider libraries licensed under Apache or MIT instead.

What legal risks exist if I reference a GPL smart contract in my Web3 project?

The main risk is potential legal action from original authors for copyright infringement. While smart contract law is still evolving, courts in many jurisdictions have upheld the enforceability of GPL obligations—violating them could result in damages. Additionally, if you seek funding or acquisition, investors may hesitate due to perceived GPL risks. Engage legal counsel early or choose less restrictive licenses to reduce exposure.

Why do people say the GPL “contaminates” my project?

This is a common way to describe the “viral” effect of the GPL. Once you include GPL code in your project—even indirectly—the entire project may need to comply with GPL terms (in certain cases). For developers wishing to keep their code proprietary, this “forced openness” feels like their project has been “contaminated.” This is not a flaw but an intentional design—to protect free software principles.

If my project only calls a GPL library’s API, do I need to open source my project?

It depends on how you interact with the library and which version of the GPL applies. If you only call APIs dynamically (e.g., external service calls), you typically do not need to open source your project. However, static linking or modifying and then using GPL code would require releasing your project’s source under the GPL. Consult an open-source attorney to clarify what qualifies as a “derivative work” and avoid legal ambiguity.

What happens if I use both GPL and MIT-licensed code in one project?

You must comply with both licenses—which can be complex. The GPL mandates open-sourcing all derivative works; MIT allows closed-source use—these terms conflict. In practice, your project must adhere to the “stricter” license (GPL) for compatibility. Avoid mixing licenses when possible or clearly separate modules by license type to reduce compliance challenges.