Regex Tester and Debugger
Paste a pattern, set flags, test against text, see matches and groups with live highlighting.
Results will appear here
If you have ever searched for “online regex tester” or “regex debugger” you probably needed a quick way to test a pattern without firing up an IDE or installing anything. This Regex Tester and Debugger tool lets you paste text, add a pattern, select flags like g or i, and instantly see matches, capture groups, and a highlighted preview. Everything runs in your browser. No signup. No data leaves your device.
Regular expressions can look scary, but with this tool you can experiment safely, see results instantly, and learn regex step by step.
Do not get lost! Hit Ctrl+D (Windows) or Command+D (Mac) to bookmark this tool for instant access.
What Is a Regex Tester?
A regex tester is a browser-based tool that allows you to write a regular expression (regex), apply it to some input text, and see what matches. Regex is short for regular expression, a syntax that defines search patterns for text.
This tool supports all JavaScript-style regex features:
- Character classes like [a-z] or \d
- Anchors like ^ and $
- Quantifiers like *, +, ?, and {n,m}
- Grouping and capture groups with ( )
- Flags like global (g), case-insensitive (i), multiline (m), dotall (s), unicode (u), sticky (y)
With the debugger, you not only see which parts matched, but also the index position and any capture groups inside.
Why Use a Regex Tester Online?
You might wonder, “Why not just test regex inside my programming editor?”
Because sometimes you need:
- A fast, no-setup environment without coding
- Learning and debugging: regex is notoriously tricky. Seeing matches highlighted helps you learn faster.
- Cross-platform: this tool works on mobile, tablet, or desktop browsers
- Safe sandbox: you can test without running any program or hitting a server
For example, if you are validating emails, scraping URLs, or checking log files, you can paste your sample text and tweak patterns until they behave exactly as you want.
How to Use This Regex Tester (Step by Step)
- Paste your sample text into the input box
- Enter a regex pattern, for example: (\w+)@(\w+\.[a-z]{2,})
- Select flags (g for global, i for case insensitive, etc.)
- Click Run
- See matches in two ways: 1. Matches list: index, full match, capture groups, 2. Highlighted preview: text with yellow for matches and green for groups
Example input text:
Contact us at [email protected] or [email protected]
Regex:
(\w+)@(\w+\.[a-z]{2,})
Flags:
g
Result:
- Match #1 at index 12: [email protected] (group1: help, group2: example.com)
- Match #2 at index 34: [email protected] (group1: support, group2: test.org)
Example Patterns You Can Try
The tool has quick chips for common patterns. Here are more practical examples:
1. Email addresses:
\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Z|a-z]{2,}\b
2. URLs:
https?:\/\/[^\s]+
3. Hex colors:
#[0-9a-fA-F]{6}
4. US phone numbers:
(\d{3})\s\d{3}-\d{4}
5. IP addresses:
(IPv4) \b(?:\d{1,3}.){3}\d{1,3}\b
These are all testable with the live highlighter.
Features of This Regex Debugger
- Enter any regex and instantly run it
- Supports all JavaScript regex flags (g, i, m, s, u, y)
- Shows matches with index positions
- Displays capture groups for advanced debugging
- Live highlighted preview with colors for matches and groups
- Quick buttons for common regex patterns
- Copy matches with one click
- Everything runs locally in your browser
Regex Basics: A Quick Refresher
If you are new, here is a mini guide:
- . (dot) matches any character
- \d matches digits 0-9
- \w matches letters, digits, and underscore
- \s matches whitespace
- ^ and $ match start and end of a line
- * means zero or more
- + means one or more
- ? makes something optional
- {n,m} means between n and m times
- () captures a group
- | is OR
Example:
Regex: (\d{4})-(\d{2})-(\d{2})
Matches: 2025-08-28 with groups: year=2025, month=08, day=28
Real-World Regex Debugging Examples
Find duplicate words:
\b(\w+)\s+\1\b
Matches “the the” or “test test” in text.
Extract hashtags from social posts:
#\w+
Matches #coding, #life, etc.
Validate a simple password rule:
^(?=.[A-Z])(?=.\d).{8,}$
Requires at least 1 uppercase, 1 digit, minimum length 8.
Pull dates like 2025-08-28:
\d{4}-\d{2}-\d{2}
Why Regex Matters
Regex is a universal skill across coding, data, and text processing. It works in JavaScript, Python, Java, C#, shell scripts, and even text editors like VS Code and Sublime. Learning it once pays off everywhere.
But regex is also hard to debug in your head. This is why a Regex Tester and Debugger is one of the most searched-for developer tools.
Frequently Asked Questions (FAQs)
Q: What is a regex tester tool?
A: It is an online tool that lets you type a regex pattern, apply it to sample text, and see matches instantly.
Q: Can I use this to learn regex?
A: Yes. By typing patterns and seeing results, you learn much faster.
Q: Is my text safe?
A: Yes. Everything runs locally in your browser. No data is sent anywhere.
Q: Which regex engine does it use?
A: It uses the JavaScript regex engine built into your browser.
Q: Does it support multiline regex?
A: Yes. Select the m flag to test multiline input.
Q: Can I see capture groups?
A: Yes. The tool lists groups separately for each match.
Best Practices for Regex Debugging
- Start small: test a single piece, then expand
- Use anchors (^ and $) when you want exact line matches
- Always test with multiple sample texts
- Watch out for greedy quantifiers (.*) that match too much
- Use groups () for clarity, not just capturing
Thank You Note
If you made it this far, you probably really needed this tool. I hope it saved you time and maybe even a bit of frustration. I keep building new tools every week, some small and some surprisingly powerful. You can check out all our free tools here and make sure to bookmark CodeForGeek so you never lose us.
If you have an idea for improvement or something is not working right, just email me at [email protected]. I actually read those messages, and if your suggestion makes sense, I will add it.
Thanks for sticking around till the end. Now go try out your result before you forget why you came here.
