Regular Expression AST Explorer
See how a JavaScript regular expression is built. Explore its parts in a tree and find syntax errors without running the pattern.
Does this tool execute my regular expression?
The pattern is parsed into a syntax tree without matching it against text. You can inspect captures and their offsets, identify syntax errors, and download the structural report.
Your result
A little clarity, right here.
Start with your own content or load the example. Your result will appear here.
Three simple steps
How to use Regular Expression AST Explorer
Choose your input and adjust the options.
Review the preview and run the tool.
Download the result and keep your original.
Common questions
Good to know
Understand the result.
Keep the original.
Is this tool free, and are my files uploaded?
This tool is free with no account required. The work happens in your browser. Your input and files are not sent to a processing server.
What are the limits and details?
Use a JavaScript regex literal including its slashes and flags, up to 10,000 characters. The syntax tree is capped for preview. Parsing does not establish that a pattern is fast or safe to execute on arbitrary text.
Limits: 500,000 characters per text field; files up to 20 MB each, 10 files and 50 MB total. Processing stops after 30 seconds.