Quick Answer
A regex tester is a scratchpad for regular expressions: you type a pattern and some sample text, and the tool highlights every match as you go. Invalid patterns are explained instead of silently failing, and each match shows its position.
What This Tool Does
Enter a pattern (with or without slashes), pick flags like g, i and m, and paste test text. Matches are highlighted inline in the test view, counted live, and listed below with their positions. A broken pattern shows the exact error message instead of crashing.
Key Features
- Live highlighting — matches glow inside the test text as you type.
- Match counter and list — know how many matches, where they start and end, and what each capture group captured.
- Independent flags — toggle
g,i,m,s,uandyin any combination. - Preset patterns — one click loads an email, URL, phone, date, IPv4 or hex-color pattern with sample text.
- Replacement preview — type a replacement like
$1-$2and see the result instantly. - Pattern breakdown — the tool explains common tokens in your pattern as you type.
- Cheat sheet — a built-in quick reference for regex syntax.
- Friendly pattern errors — invalid syntax is explained, not swallowed.
How to Use the Regex Tester
- Type your pattern — with or without surrounding slashes, or load a preset.
- Toggle the flags you need (
gis on by default). - Paste test text below.
- Watch matches highlight live; check the count, positions, and capture groups in the list.
- Optionally type a replacement to preview find-and-replace output.
Use Cases
- Validating emails, phone numbers or URLs before shipping the code.
- Building a find-and-replace pattern for a large codebase.
- Learning regex by experimenting with live feedback.
Tips
- Anchor your pattern (
^...$) when validating whole strings — most accidental matches come from missing anchors. - Use non-greedy
*?or+?when matching inside HTML or JSON. - Test empty and edge-case inputs, not just the happy path.
Privacy
Everything runs locally — your patterns and text never leave the browser.
Conclusion
Regex is powerful and unforgiving. Test it here with instant feedback before it touches production — free and private.