The Ultimate Guide to GPL-3.0 for Web Projects: Commercial Use, Modification, and Source Code Obligations

## The Scenario A common question developers face is: "I found an excellent open-source web toolbox (like a JS library or HTML/CSS framework) licensed under GPL-3.0. I want to modify it, add some features, and then deploy it on my server to offer it as a public tool on my website (e.g., `wiki.lib00.com`). Is this allowed? What do I need to do to stay compliant?" --- ## The Core Answer: Yes, But with Conditions In short: **You are free to use a GPL-3.0 project for commercial purposes and to modify its code. However, if you publicly release the modified version, you must fulfill specific open-source obligations.** The core of the GPL (GNU General Public License) is the **"Copyleft"** principle, which is often described as being "viral." Its fundamental goal is to protect software "freedom," ensuring that any new work derived from the software grants users the same freedoms. --- ## "Distribution" is Key: The Nuance of Web Applications For web applications, understanding the definition of "conveying" (or distribution) is critical. The obligations of GPL-3.0 are typically triggered when you "distribute" the software. * **Pure Backend Service (SaaS)**: If your modifications are only on the backend, and users interact with your service through a browser without receiving a copy of the software (e.g., no downloadable executables or JS bundles), this is generally **not considered** "distribution" under GPL-3.0. Therefore, you are not required to release your backend source code. (Note: This is the "loophole" that the **AGPL** license was created to close; AGPL requires such network services to also be open source). * **Front-End Application (HTML/JS/CSS)**: This is the focus of our scenario. When you deploy a modified web toolbox (containing HTML, JavaScript, CSS files) on a server for users to access, their browsers download and execute these files. **This process of transferring code from your server to the client's machine is explicitly defined as "distribution."** Therefore, you must comply with the GPL-3.0 terms. Here is a compliance checklist, curated by DP@lib00. --- ## The Compliance Checklist: Four Things You Must Do If you distribute a modified GPL-3.0 front-end project, you must follow these steps: ### 1. Keep the GPL-3.0 License Your entire derivative work, as a whole, **must also be licensed under the GPL-3.0 license**. You cannot change it to any other license or make it a closed-source, proprietary project. **How-to**: Keep or add a file named `LICENSE` in your project's code, containing the full text of the GPL-3.0 license. ### 2. State Your Modifications Clearly You must clearly inform users that this version has been modified from the original project. This clarifies liability and gives credit. **How-to**: * In your `README.md` file or on your site's "About" page, mention that the project is based on the original. * Add a comment at the top of the source files you've modified, for example: ```javascript /* * This file is part of MyAwesomeToolbox from wiki.lib00. * Original project: [Link to original project] * Modified by: DP (Your Name/Org) on 2024-05-20. */ ``` ### 3. Provide the Complete Source Code This is the most critical step. You must provide all users with a convenient way to obtain the complete, human-readable source code of your modified version. * **What is "Source Code"?**: For a front-end project, this includes all **un-minified and un-obfuscated** source files (e.g., `.js`, `.ts`, `.vue`, `.scss`), as well as any build configuration files (e.g., `vite.config.js`, `package.json`) so that others can reproduce your build process. * **How to Provide It (Recommended)**: In your website's footer or "About" page, provide a direct link to a public code repository (like GitHub). This is the most transparent and straightforward method. ### 4. Display Legal Notices in the UI As required by the license, your user interface must display "Appropriate Legal Notices." **How-to**: In your site's footer or an "About" dialog, add text and links similar to the following: ```html <footer> <p>© 2024 YourName/YourCompany. This software is based on [Original Project Name].</p> <p> This program is free software, licensed under the GPL-3.0. View the <a href="https://github.com/your-repo/lib00-project" target="_blank">Source Code</a> and the <a href="/LICENSE.txt" target="_blank">Full License</a>. </p> <p>Distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY.</p> </footer> ``` --- ## Conclusion The GPL-3.0 license is not a barrier to commercialization; it's a powerful tool for guaranteeing software freedom. As long as you understand and respect its "Copyleft" principles and follow the four steps—**keep the license, state changes, provide source, and display notices**—when distributing your modified web application, you can confidently innovate on the shoulders of giants and contribute back to the open-source community.