What is a regular expression (regex)?

A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for string matching, validation, search-and-replace, and text extraction in programming.

What regex flags are supported?

All JavaScript regex flags are supported: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode), and d (indices). Combine flags as needed.

Can I test regex for other languages like Python or PHP?

This tester uses the JavaScript RegExp engine. Most basic patterns work across languages, but advanced features (like lookbehind in older JS) may differ. For language-specific syntax, verify in your target environment.

Do I need to include slash delimiters?

No. Enter only the regex pattern, such as \d+ or [a-z]+. Put flags like g, i, or m in the separate flags field.

Is this regex tester private?

Yes. Regex testing runs in your browser. Your pattern and test text are not sent to a server.

Regex Tester Online

Pattern

Flags

Test String

What Is a Regular Expression?

A regular expression (regex) is a powerful pattern-matching syntax used in virtually every programming language. Regex patterns let you search, validate, extract, and replace text with precision. Our online regex tester lets you write a pattern, test it against sample text, and see every match highlighted in real-time—before you commit it to your codebase.

Key Features

🔎

Real-Time Matching

See matches update instantly as you type your pattern or test string. Zero delay.

🎯

Match Details

View match count, each match value, and the index position in the input string.

⚓

All JS Flags

Supports g, i, m, s, u, and d flags for full regex power.

How to Use the Regex Tester

Enter Your PatternType your regex in the Pattern field. No slashes needed. Example: \d+ matches numbers.

Set FlagsAdd flags like g (global), i (case-insensitive), or m (multiline) in the Flags field.

Paste & See MatchesPaste your test string. Matches appear instantly with each match value, index, and total count.

Common Regex Patterns

Email Validation

Pattern: ^[\w.-]+@[\w.-]+\.\w{2,}$ matches standard email addresses like user@example.com.

URL Matching

Pattern: https?:\/\/[\w.-]+(?:\/[\w./?%&=-]*)? matches HTTP and HTTPS URLs.

Phone Numbers

Pattern: \+?\d{1,3}[-.\s]?$?\d{1,4}$?[-.\s]?\d{3,4}[-.\s]?\d{4} matches international phone formats.

IP Address

Pattern: \b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b matches IPv4 addresses like 192.168.1.1.

Regex Syntax Guide

Character Classes

Use \d for digits, \w for word characters, \s for whitespace, and custom classes like [A-Z] for specific ranges.

Quantifiers

Use *, +, ?, and {n,m} to control how many times a token should match.

Groups and Alternatives

Use parentheses to group patterns and | for alternatives, such as cat|dog or (jpg|png|webp).

Anchors

Use ^ for the start, $ for the end, and \b for word boundaries when you need exact matching.

Regex Tester Use Cases

Form Validation

Test email, phone, ZIP code, slug, username, and password patterns before adding them to forms.

Log Parsing

Extract timestamps, IDs, IP addresses, request paths, status codes, and error messages from logs.

Search and Replace Prep

Validate a pattern before using it in an editor, script, CI job, or data cleanup workflow.

Developer Documentation

Create tested regex examples with sample strings for API docs, readme files, and team guidelines.

Frequently Asked Questions

What regex engine does this tester use?

It uses the native JavaScript RegExp engine built into your browser. This supports all ECMAScript regex features including lookaheads, lookbehinds, named groups, and Unicode properties.

What does the global (g) flag do?

The g flag enables global matching, finding all occurrences in the text instead of stopping at the first match. Without it, only the first match is returned.

How do I match across multiple lines?

Use the m (multiline) flag to make ^ and $ match the start/end of each line. Use the s (dotAll) flag to make . match newline characters.

Will my regex work in Python/Java/PHP?

Most basic regex patterns are portable across languages. However, advanced features like lookbehind syntax, possessive quantifiers, and atomic groups may vary. Always test in your target environment.