Features

Test and debug regular expressions in real time with live match highlighting. Supports JavaScript regex syntax, replacement patterns, and match groups. No signup, no upload — works entirely in your browser.

Regex Tester runs a regular expression against sample text and shows every match, its capture groups and a highlighted result, with support for replace mode and ready-made patterns.

When You Need This

Common pain points this tool solves

1. Checking a validation pattern before shipping it in production code.
2. Extracting email addresses, phone numbers or URLs from a block of text.
3. Debugging why a greedy quantifier swallows more than expected.
4. Testing a rewrite rule for a log processor or data pipeline.
5. Learning how capture groups work by seeing them highlighted live.
6. Confirming a search-and-replace pattern before running it across a codebase.

How to Use

Step-by-step instructions

1. Type or paste your regular expression into the pattern field.
2. Toggle the flags you need: g for global, i for case-insensitive, m for multiline, s for dot-all and u for Unicode.
3. Paste the sample text you want to test against.
4. Review the highlight, the match count and the capture groups listed for each match.
5. Switch on replace mode and enter a replacement string to preview the rewritten text.
6. Use a built-in template if you want a working email, phone or URL pattern to start from.

How it works

Step-by-step instructions

1. Enter the pattern. Write the regular expression without the surrounding slashes, and watch for syntax errors flagged as you type.
2. Set the flags. Global, case-insensitive, multiline, dot-all and Unicode flags can be toggled independently.
3. Add test text. Paste real sample data so the matches reflect the input the pattern will actually meet.
4. Inspect the matches. Check the match list, the numbering and the capture groups to confirm the pattern captures what you expect.
5. Preview a replacement. Turn on replace mode, enter the replacement, and copy the rewritten result if it looks right.

By the numbers

Flags

g, i, m, s and u

Match output

Highlighted matches, count, index and capture groups

Replace mode

Live preview of the rewritten text

Starter templates

Email, phone, URL and more

Processing

In the browser using the native RegExp engine

How we compare

Why Choose Korelyy

What makes us better

1. Live highlighting makes it obvious when a greedy quantifier or a missing anchor goes wrong.
2. Capture groups are listed per match, which is the fastest way to debug a complex pattern.
3. Replace mode previews the result before you touch real data.
4. Starter templates save you from retyping well-known patterns by hand.
5. Flags can be toggled one at a time so you can see exactly what each one changes.
6. The pattern is evaluated by the browser native RegExp engine, so the behaviour matches JavaScript.

Monetize With This Tool

Turn this tool into a side income stream

1. Use this tool to speed up your freelance work and take on more paying clients
2. Create polished content faster for your blog, YouTube channel, or social media and grow your audience
3. Offer this tool's capabilities as a service on Fiverr, Upwork, or to your local business clients

Frequently Asked Questions

1. Is Regex Tester — Test Regular Expressions Online free to use?

   Yes. Regex Tester — Test Regular Expressions Online is 100% free for core features — no signup, no watermarks, no hidden paywalls on the tools you need day to day.

2. Do I need to sign up to use Regex Tester — Test Regular Expressions Online?

   No. Open and use instantly in your browser. Nothing to install, no account required. Your preferences stay on your device.

3. Is my data safe with Regex Tester — Test Regular Expressions Online?

   Yes. Regex Tester — Test Regular Expressions Online runs locally in your browser whenever technically possible — sensitive inputs are processed on your device, not on our servers. No tracking cookies.

4. Which devices does Regex Tester — Test Regular Expressions Online work on?

   Phones, tablets and desktops with any modern browser (Chrome, Safari, Edge, Firefox). Touch-friendly and responsive from 320px to 4K.

5. How do I test a regex pattern against multiple strings?

   Enter your regex pattern in the top field and add multiple test strings separated by new lines in the test area. The tool highlights matches in real-time and shows capture groups. You can also toggle flags like global (/g), case-insensitive (/i), and multiline (/m).

6. What regex flavors does this tester support?

   This tester uses JavaScript/ECMAScript regex syntax, which covers most common patterns used in web development. It supports lookahead/lookbehind assertions, named capture groups, and Unicode property escapes.

7. Can I save and share my regex patterns?

   Yes, you can save patterns to your browser local storage and come back to them later. You can also copy the regex as a shareable URL to send to colleagues.