How does the Eclipse Public License (EPL) handle modifications?

The Eclipse Public License (EPL) requires that modifications to the original licensed code be shared under the same license when distributed. If you make changes to an EPL-licensed project and distribute the modified version, you must provide the source code of those changes under the EPL. This ensures that improvements to the original work remain open and accessible to the community. For example, if you fix a bug in an EPL-licensed library and distribute the updated version, you must share both the modified code and a clear description of the changes. This rule applies whether you distribute the code directly, include it in a product, or make it available as a service.

The EPL’s copyleft scope is narrower than licenses like the GPL. It applies to the original code and files you modify, but not necessarily to the entire project. If your work includes both EPL-licensed code and new, separate components, only the modified EPL files must remain under the EPL. For instance, adding a new plugin to an EPL-licensed application doesn’t require the plugin itself to be EPL-licensed unless it directly modifies or derives from the original code. This “file-based” approach allows developers to combine EPL-licensed code with proprietary or differently licensed components, provided the modified EPL parts are properly disclosed. This balance encourages collaboration while allowing flexibility in larger projects.

The EPL also addresses patent rights. Contributors grant users a license to any patents related to their contributions, which extends to modifications. If you modify EPL-licensed code and distribute it, you automatically grant recipients a patent license for your changes. This prevents patent litigation over community contributions. However, if you sue someone for patent infringement related to the original or modified EPL code, your rights to use the code under the EPL terminate. This clause protects downstream users and incentivizes fair use. For example, a company enhancing an EPL-licensed tool must ensure their modifications don’t introduce patent risks for others, fostering a more open and legally secure ecosystem.