I built a simple web page that checks whether two JavaScript regex are equivalent (i.e. match exactly the same strings). If the two regex are not equivalent, the tool shows example strings that match one regex but not the other.

The most common JavaScript regex syntax features are supported. Some more exotic features like back references are not supported. For anchors (^/$) and lookahead assertions, support is a bit wonky.

The UI is vibe coded but the algorithmic machinery underneath is completely hand written.