This website is for those who wants to learn how to understand and write regular expressions. It contains the tools for regex visualization and testing:
All expressions, including regular expressions, can be represented by trees of operators and operands, composed considering syntax rules of the language. The "Syntax tree" shows such trees.
Given a regular expression, you can select any node and see what part of the expression corresponds to it (it will be highlighted):
By clicking nodes with the right mouse button, and choosing the "Expand/Collapse" option, you can collapse inspected or unneeded part of the tree. It is still selectable:
The graph shows possible sequences of characters. Its nodes are single characters, character sets and sequences of characters. Edges between them show sequences and alternations. Simple assertions are shown on the edges, because the dont "consume" characters and are checked between real characters. Lookaround assertions are shown as forks with green edges.
This is a simple tool, similar to another tools of this kind. In the textarea you can enter test strings, one per line. After clicking on the "Test" button, all found matches are highligted.