What is RegEx Visualizer
RegEx Visualizer is a free JavaScript regex tester that highlights matches live, explains tokens, steps through the match engine, previews replacements, diffs two patterns, and stores local unit-test cases — all with your browser’s RegExp engine.
Use Test mode for everyday matching, Replace to preview substitutions, and Diff to compare pattern drafts. Sidebar Presets, Cheatsheet, and History help you move faster without leaving the page. Nothing is uploaded for matching.
How to use RegEx Visualizer
- Step 1: Enter a pattern and flags. Add your expression and toggle g, i, m, s, u, or y as needed.
- Step 2: Provide a test string. Paste sample text and open Matches to walk highlights and capture groups.
- Step 3: Explain or debug. Use Explanation for token detail, or Debug for a step-through when the match path is unclear.
- Step 4: Replace, Diff, or Tests. Preview replacements, compare two patterns in Diff, or add unit cases under Tests. Copy the pattern with flags when you are done.
RegEx Visualizer Features
- Test, Replace, and Diff modes
- Live match highlighting and match stepper
- Explanation and step debugger views
- Unit-test cases (add, run all, should match)
- Flags: g, i, m, s, u, y
- Presets, Cheatsheet, and History (stored locally)
- Copy pattern with flags
Common use cases
- Validate form input patterns: Try emails, slugs, or IDs against realistic samples before shipping client validation.
- Debug a failing match: Step through Debug and read Explanation when a pattern matches too much or too little.
- Safe find-and-replace previews: Use Replace mode on sample data before changing production files.
- Compare pattern drafts: Diff two expressions when refactoring a regex with a teammate.
- Build a tiny test suite: Add should-match cases so regressions show up while you edit.
- Learn regex visually: Highlights and explanations make capture groups and quantifiers easier to understand.
Built around JavaScript RegExp in the browser:
- JavaScript regular expressions and flags
- Plain-text test strings
- Replacement strings in Replace mode
- Optional second pattern in Diff mode
- Local history and test cases in the browser
Exploring other developer utilities? Browse all tools including JSON Formatter and XML Formatter.
FAQ
Is RegEx Visualizer free?
Yes. Tools Viewer tools are free to use in the browser with no account required.
Do I need to create an account to use RegEx Visualizer?
No. Open the tool and start working — signup is not required.
Is my content uploaded to your servers?
No. RegEx Visualizer runs in your browser. Content stays on your device unless you copy or download a file yourself.
Can I export code for Python or other languages?
Matching follows JavaScript RegExp. You can copy the pattern with flags; there is no multi-language code export panel. Always re-test dialect differences in the target language.
Does lookbehind or Unicode work?
Support matches what your browser’s JavaScript RegExp engine implements. Invalid patterns surface as errors in the tool.
What is a good online regex tester?
A useful tester highlights matches live, explains tokens, supports replace previews, and runs entirely in the browser so sample data is not uploaded. RegEx Visualizer is built around that workflow for JavaScript RegExp.
How do I test a regular expression online?
Paste the pattern and a sample string into RegEx Visualizer, set flags, and review Matches. Use Explanation or Debug when the result is surprising, then Copy the pattern into your project.
RegEx Visualizer & Explainer