What Is a Regular Expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. Regex patterns are used to find, match, validate, extract, and replace text based on rules rather than exact strings. They're supported in virtually every programming language and are one of the most powerful text processing tools available to developers.
Whether you're validating an email address, extracting data from log files, finding specific patterns in thousands of lines of text, or performing complex find-and-replace operations, regex is the tool that makes it possible.
What Our Regex Tester Provides
- Real-time matching: Every match highlights as you type your pattern — no need to click "Test"
- Match details: Shows every match with its start/end position and matched string
- Capture groups: Named and numbered capture groups displayed per match
- Flags support: Toggle g, i, m, s, u flags independently
- Pattern library: 30+ pre-built patterns for email, URL, phone, date, IP, and more
- Replace mode: Test regex replacement with preview of the substituted output
How to Test a Regex Pattern
Enter Your Pattern
Type your regex in the Pattern field (without slashes). Matches highlight in the test string immediately as you type.
Set Your Test String
Paste the text you want to test against. Multi-line text is supported — paste log files, CSV data, or any real-world input.
Toggle Flags as Needed
Enable case-insensitive (i), global (g), multiline (m), or dotAll (s) flags based on your requirements.
Review Matches & Groups
All matches are listed below with positions and capture group values. Switch to Replace mode to test substitution patterns.
Common Regex Patterns — Ready to Use
| Pattern | What It Matches |
|---|---|
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ | Email address |
https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6} | URL |
^\+?[1-9]\d{1,14}$ | International phone (E.164) |
^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|...) | IPv4 address |
^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$ | Date (YYYY-MM-DD) |
Regex Flags — What Each One Does
- g (global): Find all matches, not just the first one
- i (case-insensitive): Match regardless of letter case —
Hellomatcheshello,HELLO - m (multiline): ^ and $ match start/end of each line, not just the full string
- s (dotAll): The dot (.) matches newline characters too — otherwise . skips them
- u (unicode): Enables full Unicode support, including emoji and non-Latin scripts
Test Regex Patterns Free
Real-time highlighting, capture groups, flags, replace mode, and 30+ pattern library.
Open Regex TesterCapture Groups and Named Groups
Capture groups (pattern) isolate parts of a match for individual extraction. Named groups (?<name>pattern) make groups easier to reference. Our tester shows the value of each numbered and named group for every match — essential for debugging complex extraction patterns.
ToolMatrix Regex Tester
Real-time match highlighting, match list with positions, capture group breakdown, all regex flags, replace mode with live preview, and a 30+ pattern library for common validations. Free, browser-based, no account needed. All regex processing happens locally — your test data stays private.