Regex Tester & Pattern Builder
Test and debug regular expressions in real time with live match highlights, capture group breakdown, and pattern templates.
| # | Match Value | Index Range | Capture Groups |
|---|---|---|---|
| Matches will list here... | |||
The Complete Guide to Regular Expressions (Regex)
Regular Expressions (Regex) are powerful search patterns used across programming languages (JavaScript, Python, Java, PHP, Go, C#) to parse strings, validate user input (emails, phone numbers, passwords), extract structured data, and perform automated search-and-replace refactoring.
How to Use
- Define Pattern: Enter regex expression into the top input bar.
- Select Flags: Toggle
g(global),i(case-insensitive), orm(multiline). - Input Sample: Paste target text string into the test text window.
- Analyze Matches: Review highlighted matches and captured sub-groups.
100% Client-Side Evaluation
Evaluation runs 100% inside your local browser's V8 JavaScript engine. Your test strings, code snippets, and customer datasets are never transmitted over network connections.
Quick Regex Syntax Reference Cheatsheet
Character Classes
\d : Any Digit (0-9)
\w : Word Char (a-z, A-Z, 0-9, _)
\s : Whitespace (space, tab, newline)
Quantifiers
* : 0 or more
+ : 1 or more
? : 0 or 1 (Optional)
{n,m} : Between n and m
Anchors & Boundaries
^ : Start of string
$ : End of string
\b : Word Boundary
Groups & Logic
(abc) : Capture Group
(?:abc) : Non-capturing Group
a|b : Either a or b
Frequently Asked Questions
What do the regex flags mean?
Flags alter search behavior: g (global) finds all matches instead of stopping after the first match; i (ignore case) ignores uppercase vs lowercase; m (multiline) treats ^ and $ as line starts/ends; s (dotAll) allows . to match newlines.
How do capture groups work in Regex?
Parentheses (...) create capture groups that extract specific sub-parts of a matched pattern (such as isolating domain names from email addresses or area codes from phone numbers).