AST Exploring Tool

ExtendJ Explorer is an interactive tool for exploring the ASTs built by ExtendJ.

The tool shows a graphical view of the parsed AST alongside the Java source code, and it even lets you inspect attributes for particular nodes in the AST!

The AST can be filtered based on a flexible filter rule language.

Here is a screenshot of the application in use:

ExtendJ Explorer Screenshot

The latest version of ExtendJ Explorer can be downloaded here:


Java source code can be loaded or typed directly in the source viewer inside the visualizer. Click the "Rebuild AST" button to refresh the tree view after editing the source code.

Filtering nodes

A filter can be entered in the filter editor. The filter language consists of three different kinds of rules:

  • include - includes matched nodes in the filtered tree
  • exclude - filters out the matched nodes, and their subtrees
  • set - only used to change properties for matched node

Each rule has a path pattern consisting of the type names for nodes on the path from the tree root, or wildcard expressions.

Each rule can also provide a matching condition based on node attributes, and add style and attribute info for the matched nodes.


The tool requires Java 8 update 40 or later to run.

On Ubuntu, the openjfx package is required when using OpenJDK. The package may be installed by running this command in a terminal:

sudo apt-get install openjfx

DrAST - A visualizer for any JastAdd project

ExtendJ Explorer is a fork of DrAST, which can be used with any JastAdd compiler - not just ExtendJ. DrAST was the Master's Thesis project of Joel Lindholm and Johan Thorsberg.