Free Online Regex Tester

Test and debug regular expressions in real time. See matches highlighted and cap...

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Regex Cheat Sheet

Characters

  • . Any character
  • \d Digit [0-9]
  • \w Word [a-zA-Z0-9_]
  • \s Whitespace

Quantifiers

  • * 0 or more
  • + 1 or more
  • ? 0 or 1
  • {n,m} n to m times

Anchors

  • ^ Start of string
  • $ End of string
  • \b Word boundary
  • \B Non boundary

Groups

  • (abc) Capture group
  • (?<n>abc) Named group
  • (?:abc) Non capture
  • [abc] Character class

Quick answer

A regex tester lets you build and check a regular expression against sample text, highlighting the matches and showing the capture groups. This one runs entirely in your browser on the native JavaScript RegExp engine, so patterns and test data are never uploaded. Type a pattern, toggle flags like g, i, m, s, u and y, and watch matches highlight live with numbered and named groups plus a replace preview.

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Tester Features

Match Highlighting - Matches are highlighted in yellow in real-time
Capture Groups - View each capture group with index and content
6 Flag Options - Global, case insensitive, multiline, dotall, unicode, sticky
Replace Preview - Test substitutions with group references ($1, $2)
Common Patterns - Pre-built patterns for email, URL, phone, IP, date, hex
Cheat Sheet - Quick reference for characters, quantifiers, anchors, groups

Why Use Free Online Regex Tester?

Real-Time Matching

See matches highlighted instantly as you type. No need to click buttons or wait for results.

Capture Group Details

View each capture group separately with clear labeling. Perfect for complex patterns with multiple groups.

Replace Mode

Test find-and-replace operations with group references ($1, $2). Preview the result before using in your code.

Built-in Cheat Sheet

Quick reference for common regex syntax. Character classes, quantifiers, anchors, and groups at a glance.

Common Uses for Regex Tester

Email Validation

Test and refine email validation patterns for forms and input fields.

Code Refactoring

Build find-and-replace patterns for bulk code changes across files.

Log Parsing

Extract specific data from log files using capture groups.

Input Sanitization

Create patterns to validate and sanitize user input in applications.

How It Works

1

Enter Your Pattern

Type your regular expression in the pattern field. Use the common patterns buttons for quick templates like email or phone validation.

2

Configure Flags

Select flags to modify matching behavior. Use Global to find all matches, Case Insensitive for flexible matching, or Multiline for line based patterns.

3

Test and Refine

Enter test text to see matches highlighted in real-time. View capture groups in the details panel. Enable replace mode to test substitutions.

Regex Tips

Start Simple

Build your regex incrementally. Start with a simple pattern that matches broadly, then add specificity. Test each change in real-time.

Use Common Patterns

Click the pre-built pattern buttons for email, URL, or phone validation as starting points, then customize for your specific needs.

Escape Special Characters

Characters like . * + ? { } [ ] ( ) | \ ^ $ have special meaning in regex. Use a backslash (\) to match them literally.

Frequently Asked Questions

Type your pattern into the regex field, pick any flags you need, then paste sample text into the test string box. Matches highlight instantly and the details panel lists each match with its start index and capture groups. Nothing is sent to a server, so it works offline and on private data.
Flags change how a pattern matches. g (global) finds every match instead of stopping at the first, i ignores case, m makes ^ and $ match at the start and end of each line, s lets the dot match newlines, u turns on full Unicode handling, and y (sticky) matches only from the current position. Toggle them with the flag buttons.
Wrap part of a pattern in parentheses to capture it. Each group is numbered left to right, so (\w+)@(\w+) captures the name in group 1 and the domain in group 2. You can also name a group with (?<name>...). In replace mode, reference them with $1, $2, or $<name>.
The usual causes are an unescaped special character (use \. for a literal dot), a missing g flag when you expect more than one match, or case sensitivity when you meant to add i. If the pattern is malformed, this tester shows a plain error message instead of matches so you can fix the syntax.
It uses the browser's native JavaScript RegExp engine, so results match how regex behaves in Node.js and front end code. The core syntax lines up with most languages, though lookbehind, named groups, and Unicode property escapes can differ in older engines like PCRE or Python.
Yes. It highlights matches live, breaks out numbered and named capture groups, previews replacements with $1 style references, and ships common presets for email, URL, phone, IPv4, date, and hex color. It runs fully client side with no account, so your patterns and test data never leave your device.

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