JavaParser is an open-source project built by volunteers. We welcome all contributions.
Development is performed on GitHub. This is the page of projects:
You are already familiar with GitHub
You can find information specific to JavaParser by looking at our contributing guidelines.
You are not familiar with GitHub
We suggest looking at this introduction to GitHub.
If you want to contribute feel free to ask questions on our gitter channel or open an issue (here for JavaParser, here for JavaSymbolSolver). Our community will help you and guide you to start contributing.