Indeetools

Free Online Regex Tester & Regex Builder

Test and debug regex patterns instantly with real-time visual feedback. Perfect for developers who need a reliable regex checker online to validate patterns before implementation. Our free regex tester shows matches, capture groups, and errors as you type, making it the ideal JavaScript regex tester for debugging complex patterns.

Common Patterns
Select a pattern to use
Regex Pattern
Enter your regular expression pattern and select flags

Find all matches

Ignore case

Treat as line break

Dot matches newline

Unicode support

Match at exact position

Test String
Enter text to test your regex against
Results
No matches found
Enter a regex pattern and test string to see results.

What This Tool Does & Why It's Useful

Purpose: This regex builder and tester lets you create, test, and debug regular expressions in real-time. No more guessing if your pattern works - see matches highlighted instantly.

Privacy: Everything runs 100% in your browser. Your test data, patterns, and sensitive information never leave your device, making it safe for production debugging.

Who it's built for: Developers, QA engineers, data analysts, students, and anyone working with text validation or extraction.

Immediate benefits: Get instant visual feedback, avoid common regex mistakes, and export patterns in multiple programming languages with proper escaping.

Key Features

1. Real-Time Testing

See matches highlight instantly as you type. Perfect for debugging complex patterns on the fly.

2. Capture Groups Visualization

View all capture groups, their values, and match positions. Essential for data extraction tasks.

3. Regex Flags

Toggle g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode), and y (sticky) flags with a single click.

4. Multi-Language Export

Export your validated regex to JavaScript, Python, PHP, Java, C#, Node.js, or Go with automatic escaping.

5. Pattern Library

Quick access to common patterns: email, phone, URL, IP address, dates, credit cards, and more.

6. Privacy First

All processing happens locally in your browser. No server uploads, no data tracking.

How to Use This Tool

  1. Enter your pattern: Type or paste your regex in the Pattern field
  2. Test against text: Add your sample text in the Test String field
  3. Adjust flags: Toggle regex flags to modify matching behavior
  4. View results: See matches highlighted and capture groups extracted
  5. Export when ready: Copy the pattern or export for your programming language

Examples You Can Try

Email Validation

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[A-Za-z]{2,}$

Phone Number Extraction

\b\d{3}[-.]?\d{3}[-.]?\d{4}\b

HTML Tag Matching

<[^>]+>

Date Format Detection

\b\d{1,2}[\/\-]\d{1,2}[\/\-]\d{4}\b

Credit Card Pattern

\b(?:\d{4}[-\s]?){3}\d{4}\b

Why This Tool Is Better Than Other Regex Testers

⚡ Speed: Instant matching with zero latency. No server requests means immediate feedback as you type.
🔒 Privacy: Your data never leaves your browser. Unlike other tools that may track or store your patterns, ours is 100% client-side.
📋 Pattern Presets: One-click access to validated patterns for common use cases. No need to reinvent the wheel.
🌐 Multi-Language Export: Export to 7+ programming languages with proper escaping. Unique feature not found in most regex testers.
💎 Modern UI: Clean, responsive design that works perfectly on desktop, tablet, and mobile.

Long-Tail Keywords & Search Intent

Need to check regex patterns online? Our tool provides real-time validation with visual feedback, making it easy to understand exactly what your pattern matches. When you're debugging complex expressions, this online regex checker helps identify issues instantly without running code.

As a JavaScript regex tester, it perfectly simulates how your patterns will behave in Node.js or browser environments. For those working with Python or PHP, the multi-language export feature ensures your patterns work correctly across different regex engines.

Use our regex debugger to step through complex patterns and understand why they're not matching as expected. Whether you're validating form inputs, parsing log files, or extracting data from text, this tool makes regex testing intuitive and efficient.

Who Should Use This Tool

👨‍💻 Developers

Build and validate regex for form validation, API input sanitization, and text processing

🔍 QA Engineers

Test input validation patterns and edge cases in applications

🎓 Students

Learn regex concepts with visual feedback and instant examples

📊 Data Analysts

Extract patterns from logs, documents, and datasets efficiently

🖥️ Sysadmins

Parse log files and configuration files with custom patterns

🛡️ Security Engineers

Test input validation patterns and search for vulnerabilities

Understanding Regular Expressions

Common Regex Patterns

Use CasePattern
Email[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[A-Za-z]{2,}
Phone (US)\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}
URLhttps?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)
IP Address\b(?:\d{1,3}\.){3}\d{1,3}\b

Regex Quantifiers

QuantifierDescription
*Zero or more occurrences
+One or more occurrences
?Zero or one occurrence (optional)
{n}Exactly n occurrences
{n,}n or more occurrences
{n,m}Between n and m occurrences

Regex Tips & Best Practices

• Escape special characters with backslash: \., \*, \+, \?, \[, \], \{, \}, \(, \)

• Use ^ for string start and $ for string end anchors

• \d matches digits (0-9), \w matches word characters (a-z, A-Z, 0-9, _)

• Use lazy quantifiers (*?, +?) to match the smallest possible string

• Test edge cases: empty strings, boundary conditions, special characters

Regex Flags Guide

g (global): Find all matches, not just the first one

i (case-insensitive): Match uppercase and lowercase equally

m (multiline): ^ and $ match start/end of each line

s (dotall): . matches newlines too

u (unicode): Enable full Unicode support

y (sticky): Match only from the current position

Common Use Cases

Email Validation

Validate email formats in forms, user registration, and contact forms

Phone Number Formatting

Extract and validate phone numbers in various formats

Date Pattern Matching

Parse dates in different formats for data processing

URL Extraction

Find and extract URLs from text content

Frequently Asked Questions

Is this regex tester completely free?

Yes, no registration or payment required. Free forever with all features.

Is my test data and privacy safe?

Absolutely. Everything runs in your browser. No data is sent to any server.

Does it work on mobile devices?

Yes, fully responsive and optimized for mobile, tablet, and desktop.

Which programming languages does it support?

JavaScript, Python, PHP, Java, C#, Node.js, Go, with more added regularly.

Can it handle complex regex with lookaheads?

Yes, supports all modern regex features including lookaheads, lookbehinds, and atomic groups.

Are there any limitations on pattern size?

No strict limits, but very large patterns may affect performance in some browsers.

Related Tools

If you're working with text processing and data manipulation, you might also find these tools useful:

Base64 Encoder/Decoder
JSON Validator
URL Encoder/Decoder
Hash Generator
Text to Size Converter
Color Palette Generator
CSV to JSON Converter
String Case Converter

Final Summary

Our free online regex tester provides everything you need to build and debug regular expressions efficiently. With real-time matching, capture group visualization, multi-language export, and complete privacy protection, it's the perfect tool for both beginners and professionals. Test your regex patterns instantly and export them to your preferred programming language—all from the comfort of your browser.

Common Regex Patterns Reference

Essential Regex Patterns and Their Uses

PatternDescriptionUse Case
\\dMatches any digit (0-9)Extract numbers from text
\\wMatches word characters (a-z, A-Z, 0-9, _)Validate usernames, identifiers
\\sMatches any whitespace characterFind or replace spaces, tabs
.Matches any single character except newlineWildcards, flexible matching
[a-z]Matches any lowercase letterValidate text format
+Matches one or more of the preceding elementEnsure at least one occurrence
*Matches zero or more of the preceding elementOptional or repeated elements
^Matches the start of the stringValidate beginning of string
$Matches the end of the stringValidate end of string
Understanding Regular Expressions

Regular expressions (regex) are powerful patterns used to match, search, and manipulate text. They're essential tools for developers, data scientists, and content managers dealing with text processing tasks.

Key Components:

  • Literal Characters: Match themselves exactly (e.g., "cat" matches "cat")
  • Special Characters: Have special meaning (e.g., dot ".", star "*", question mark "?")
  • Character Classes: Match one of several characters (e.g., "[abc]" matches "a", "b", or "c")
  • Anchors: Position matches at specific locations (e.g., "^" start, "$" end)
Regex Operations Explained

Matching Text

Method: Find occurrences of a pattern in text

Example: Pattern "cat" finds "cat" in "concatenate" and "caterpillar"

Extracting Data

Method: Use capturing groups (parentheses) to extract specific parts

Example: Pattern "(\\d4)-(\\d2)-(\\d2)" extracts year, month, day from "2023-12-25"

Validating Input

Method: Use anchors and strict patterns to ensure full match

Example: Pattern "^\\d5$" validates exact 5-digit zip codes

Replacing Text

Method: Find matches and replace with new content

Example: Replace "\\s+" with " " to normalize multiple spaces to single spaces
Real-World Applications

Web Development

Form validation, URL routing, parsing HTML/XML, sanitizing user input, and scraping data.

Data Analysis

Extracting structured data from unstructured text, cleaning datasets, and pattern recognition.

Security

Detecting SQL injection, cross-site scripting attempts, and validating secure password patterns.

Content Management

Finding and replacing text, formatting documents, and processing large volumes of text efficiently.

Quantifiers Reference
QuantifierDescriptionExampleMatches
*Zero or morea*"", "a", "aa", "aaa"
+One or morea+"a", "aa", "aaa"
?Zero or onea?"", "a"
{n}Exactly n timesa3"aaa"
{n,}At least n timesa2"aa", "aaa", "aaaa"
{n,m}Between n and m timesa{2,4}"aa", "aaa", "aaaa"
Tips for Working with Regex
1.
Start simple - Build complex patterns step by step, testing at each stage.
2.
Use non-capturing groups - Use (?:...) when you need grouping but not capture to improve performance.
3.
Be careful with dots - The dot (.) doesn't match newlines by default, use the /s flag to change this.
4.
Escape special characters - Use backslashes (\\) to match literal special characters in your text.
5.
Test with various inputs - Ensure your regex handles edge cases and unexpected inputs appropriately.
Common Use Cases
Email Validation:
Pattern: "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$"
Phone Numbers:
Pattern: "^\(?([0-9]{3})\)?[-.\s]?([0-9]{3})[-.\s]?([0-9]{4})$"
Date Format:
Pattern: "^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$"
URL Pattern:
Pattern: "^https?://[a-zA-Z0-9-.]+\.[a-zA-Z]{2,}(/.*)?$"
Regex Flags Guide
Global (g)g

Find all matches instead of stopping after the first

Case Insensitive (i)i

Ignore uppercase/lowercase differences

Multiline (m)m

^ and $ match start/end of each line, not just string

Dot All (s)s

Dot (.) matches newline characters too

Best Practices
  • Use character classes [A-Za-z] instead of multiple alternatives for simple matches
  • Make patterns specific enough to avoid false matches
  • Consider performance implications for very large datasets
  • Document complex regex patterns for future maintenance