Which programming languages is this compatible with?

This tool runs in your browser using JavaScript's Regex engine. Basic syntax (like \d, +, *) is compatible with PHP, Python, and Java, but advanced features (like lookbehinds) might vary slightly between languages.

Developer Tool

Regex Tester & Visualizer

Q: Why does it only match the first occurrence?

By default, Regex stops after the first match. To find all occurrences in the text, you need to add the 'g' (Global) flag in the flags input box.

Q: What are 'Capture Groups'?

Capture groups are parts of the pattern enclosed in parentheses ( ). They allow you to extract specific parts of the matched string (like extracting just the domain from an email) and reuse them with $1, $2 variables.

Solve "Write-Once, Read-Never" regex problems.
Real-time testing, explanation, and code generation in one place.

/^\d{5}$/

90210

Zip Code OK

Regular Expression

/ /

Unit Tests

*Checks if each line matches as expected.

Real-time Check

{{ sandboxMatches.length }} matches found:

Structure Visualizer

Enter a regex pattern to see its structure.

Explanation

Explanation will appear here.

Capture Groups ($1, $2...)

#	Content
${{ i + 1 }}	{{ g }}

Library

Code Gen

Click to insert:

Email Address

US Zip Code

US Phone No.

Date (YYYY-MM-DD)

URL

Strong Password

JavaScript

const regex = /{{regexPattern}}/{{flags}};
const result = regex.test(str);

PHP

preg_match('/{{regexPattern}}/{{flags}}', $str);

Python

import re
pattern = re.compile(r'{{regexPattern}}')

Common Tokens

Regex Cheat Sheet & Basic Rules

A quick reference for common regular expression metacharacters and syntax. Bookmark this for your development needs.

1. Special Characters (Metacharacters)

Symbol	Meaning	Example
.	Any character (except newline)	`a.c` → abc, aXc
\d	Digit (0-9)	`\d{3}` → 123
\w	Word character [a-zA-Z0-9_]	`\w+` → user_id
\s	Whitespace (space, tab, newline)
[ ]	Character class (any of these)	`[abc]` → a, b, or c
[^ ]	Negation (not these)	`[^0-9]` → Non-digit
\|	OR (Alternative)	`jpg\|png`
\	Escape character	`\.` → Literal dot

2. Quantifiers (Repetition)

Symbol	Meaning	Example
*	0 or more times	`a*` → (empty), a, aa...
+	1 or more times	`a+` → a, aa, aaa...
?	0 or 1 time (Optional)	`https?` → http, https
{n}	Exactly n times	`\d{4}` → 2025
{n,}	n or more times	`\d{8,}` → 8+ digits
{n,m}	Between n and m times	`\d{2,4}` → 2 to 4 digits

3. Anchors (Position)

Symbol	Meaning	Example
^	Start of line/string	`^http` → Starts with http
$	End of line/string	`jpg$` → Ends with jpg

4. Flags (Options)

Options specified after the regex pattern (e.g., /pattern/g). You can input these in the small box to the right.

Flag	Name	Behavior
g	Global	Find all matches rather than stopping after the first match.
i	Ignore Case	Case-insensitive search (matches both 'A' and 'a').
m	Multiline	^ and $ match start/end of each line, not just the whole string.

Useful Regex Snippets (Top 10)

Use Case	Pattern	Note
Email	`^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$`	Basic validation
US Zip Code	`^\d{5}(-\d{4})?$`	5 digits or 5+4
Phone (US)	`^$?\d{3}$?[-.\s]?\d{3}[-.\s]?\d{4}$`	Allows (123) 456-7890
Date (ISO)	`^\d{4}-\d{2}-\d{2}$`	YYYY-MM-DD
URL	`https?://[\w!?/+\-_~=;.,*&@#$%()'[\]]+`	Starts with http/s
Password (Strong)	`^(?=.[a-z])(?=.[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$`	8+ chars, upper, lower, digit
Username	`^[a-zA-Z0-9_-]{3,16}$`	Alphanumeric, 3-16 chars
Integer	`^\d+$`	Numbers only
Hex Color	`^#([a-fA-F0-9]{6}\|[a-fA-F0-9]{3})$`	#ffffff or #fff
Slug	`^[a-z0-9]+(?:-[a-z0-9]+)*$`	URL-friendly text

FAQ

Why does it only match the first occurrence?

By default, Regex stops searching after finding the first match. To find all instances in the text, you must enable the Global flag. Enter g in the small input box on the right side of the main regex input.

What are "Capture Groups"?

Capture groups are parts of your pattern enclosed in parentheses ( ). They allow you to isolate and extract specific parts of the matched text.

For example, in the pattern (\d{4})-(\d{2}), $1 would contain the year and $2 would contain the month. This is useful for data extraction and replacement.

Is the code valid for all languages?

This tool runs in the browser and uses the JavaScript regex engine. While basic syntax (like \d, +, *) is standard across PHP, Python, and Java, some advanced features (like lookbehinds) may differ.

Always double-check the specific documentation for your target language.