Regex Tester Live
What is a Regular Expression (Regex) and how to test it online?
A regular expression (regex) is a sequence of characters that defines a search pattern. An online regex tester lets you instantly test, debug, and validate expressions against real text — no setup needed.
Regex is used everywhere in software development: form validation, log parsing, data extraction, search and replace, URL routing, and code refactoring. Mastering regex saves hours of manual text processing.
How to use this regex tester
- Enter your regular expression in the input field (between the
/slashes) - Toggle the flags you need (g, i, m, s, u)
- Paste your test string — matches highlight in real time
- Use the pattern library to load common expressions instantly
Basic regex syntax
.— matches any character except newline*— matches 0 or more occurrences+— matches 1 or more occurrences?— matches 0 or 1 occurrence (also makes quantifiers lazy)[]— character class (e.g.[a-z0-9])()— capturing group(?:)— non-capturing group^— start of string (or line in multiline mode)$— end of string (or line in multiline mode)\d— digit,\w— word character,\s— whitespace{n,m}— between n and m occurrences
Regex flags explained
g (global) — find all matches, not just the first one.
i (ignore case) — case-insensitive matching.
m (multiline) — ^ and $ match start/end of each line.
s (dotAll) — . also matches newline characters.
u (unicode) — enables full Unicode support and stricter parsing.
Common regex use cases
- Email address validation in signup forms
- Password strength rules (length, uppercase, digits)
- Extracting dates, URLs, or IPs from log files
- Search and replace in code editors (VS Code, Vim)
- URL routing in web frameworks
- Stripping HTML tags from content
Frequently Asked Questions
A regex tester is an interactive tool that lets you test regular expressions against sample text and see matches highlighted in real time — without writing any code.
A string search finds only exact literal matches. Regex allows complex pattern matching — you can match any digit, any word character, ranges of characters, optional parts, repetitions, and lookaheads/lookbehinds.
Flags modify how the regex engine interprets the pattern. Use g to find all matches (not just the first), i when you want case-insensitive matching, m when your text has multiple lines and you need ^/$ to match each line, and s when your pattern needs . to match newline characters.
A capturing group () extracts a specific part of a match. For example, (\d{4})-(\d{2})-(\d{2}) applied to 2024-05-21 captures three groups: 2024, 05, and 21. You can then reference these groups in replacements or code. Use (?:) for a non-capturing group when you only need grouping for logic, not extraction.
Greedy quantifiers (*, +, {n,}) match as much text as possible. Lazy quantifiers (*?, +?, {n,}?) match as little as possible. For example, on the text <b>bold</b>, the greedy <.*> matches the entire string, while the lazy <.*?> matches only <b>.
No. This regex tester runs entirely in your browser via JavaScript. Your patterns and test strings never leave your machine.
This tool uses JavaScript's built-in RegExp engine (ECMAScript regex). It supports most common regex features but differs slightly from PCRE (used in PHP, Python) — notably, JavaScript does not support lookbehind in older engines and has no named backreferences in the replace syntax in some older browsers.