Free Developer Tool — 100% Client-Side

Regex Tester

Test regular expressions in real-time with match highlighting, group capture, and flag controls.

Regular Expression

/ /

Test String

2 matches

Matches

What Is a Regex Tester?

A regex tester is an interactive tool that helps developers write, test, and debug regular expressions (regex) in real-time. It shows exactly which parts of your input text match your pattern, making it invaluable for building and troubleshooting regex patterns for validation, search, parsing, and text transformation tasks.

Common Regex Patterns

Email

\w+@\w+\.\w+

Phone (US)

$\d3$\s\d3-\d4

URL

https?://\S+

IP Address

\d3\.\d3\.\d3\.\d3

Understanding Regex Flags

g — Global

Find all matches, not just the first one.

i — Case-Insensitive

Ignore case when matching letters.

m — Multiline

^ and $ match line boundaries, not string boundaries.

s — Dotall

The . metacharacter matches newlines too.

Use Cases for Regex Testing

Form Validation — Validate email addresses, phone numbers, URLs, and postal codes in web forms.
Log Parsing — Extract structured data from server logs, application logs, and error reports.
Data Extraction — Pull specific patterns from large text documents, API responses, or configuration files.
Search & Replace — Find and transform text patterns across files with regex-based substitution.
Input Sanitization — Filter and clean user input by matching allowed or disallowed patterns.

How to Use This Regex Tester

Enter your regex pattern between the forward slashes in the pattern input field. Add flags (g, i, m, s, u) using the flag buttons or the flags input. Type or paste your test string in the text area below. Matches are highlighted in real-time with colored backgrounds, and capturing groups are displayed in the groups section below the matches. If your regex is invalid, an error message will show the syntax problem.

How to Do This in Code

const regex = /hello (\w+)/gi;
const match = regex.exec('Hello World hello everyone');
// match[0] = full match, match[1] = captured group

import re
pattern = r'hello (\w+)'
matches = re.findall(pattern, 'hello world', re.IGNORECASE)

import "regexp"

re := regexp.MustCompile(`hello (\w+)`)
matches := re.FindStringSubmatch("hello world")

echo 'hello world' | grep -Eo 'hello [a-z]+'
echo 'hello world' | sed -n 's/hello \([a-z]*\)/found: \1/p'

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Regex Tester FAQ

What regex flavors are supported?

This tool uses JavaScript's RegExp engine, which follows the ECMAScript specification. It supports most common patterns including groups, lookaheads, and quantifiers.

What do the flags do?

g = global (find all matches, not just first), i = case-insensitive, m = multiline (^ and $ match line boundaries), s = dotAll (. matches newlines).

Regex Tester

Matches

Capturing Groups

What Is a Regex Tester?

Common Regex Patterns

Email

Phone (US)

URL

IP Address

Understanding Regex Flags

g — Global

i — Case-Insensitive

m — Multiline

s — Dotall

Use Cases for Regex Testing

How to Use This Regex Tester

How to Do This in Code

Popular Developer Tools

Need a Fast Code Editor?

Related Tools

JSON Formatter

Case Converter

Text Diff Checker

Regex Tester FAQ