Check regex online against sample text in real time. Highlight matches, inspect capture groups, toggle JavaScript flags, and debug patterns without leaving the page.

What is Check Regex Online - Regex Tester?

Use this online regex tester when you need to check regex online against real sample text before adding a pattern to code, forms, log filters, or data cleanup scripts. The live tester stays at the top of the page so you can paste a pattern, add test text, toggle JavaScript flags, and immediately see matches, indexes, and capture groups while you debug.

Common Use Cases

Email validation: try a practical pattern like ^[\w.%+-]+@[\w.-]+\.[A-Za-z]{2,}$ against a list of addresses before using it in a form.
Log parsing: check regex online for timestamps, request IDs, IP addresses, or error codes in pasted application logs.
Data cleanup: preview find-and-replace patterns for CSV fields, imported text, or messy scraped content before running them elsewhere.
JavaScript debugging: verify how groups, alternation, anchors, and flags behave in the same browser regex engine your frontend code uses.

Example: Input & Output

Sample Input

See the tool above for interactive examples.

Expected Output

The processed output will appear here instantly.

How to Use

Step 1: Enter the regular expression pattern you want to test—without the surrounding slashes unless the field asks for them.
Step 2: Paste realistic sample text into the test area so the online regex tester can show true matches and misses.
Step 3: Toggle flags such as global (g), case-insensitive (i), multiline (m), or dotAll (s) to match your target runtime.
Step 4: Review highlighted matches, indexes, and capture groups, then adjust the pattern until it behaves correctly.

Frequently Asked Questions

What regex engine does this online regex tester use?

This tool uses the JavaScript regex engine built into your browser, so it is best for checking patterns intended for JavaScript, TypeScript, browser forms, Node.js, and many frontend validation workflows.

How do I check regex online without risking private text?

The tester runs locally in your browser. Your pattern and sample text are not uploaded to UtilityBelt.dev, which makes it suitable for debugging snippets from logs, forms, or documents you do not want to send to a server.

Why does my regex show an invalid pattern error?

Invalid pattern errors usually come from unescaped characters, an unfinished group or character class, or syntax unsupported by the JavaScript regex engine. Start with a smaller pattern, confirm it matches, then add groups or lookarounds one at a time.

Can I use lookbehinds and capture groups?

Yes. Modern browsers support capture groups, named groups, lookaheads, and lookbehinds. If you target older runtimes, test compatibility before shipping the pattern.

Privacy & Security

All data processing for the Check Regex Online - Regex Tester happens entirely on your local machine within your browser. No data is ever sent to our servers, ensuring your information remains private and secure. We believe in privacy by design, and our tools are built to be used without compromising your data.

Check Regex Online - Regex Tester