Developer Utility
Free Regex Tester & Debugger 2026
Test regular expressions against any string — see matches, capture groups, flags, and replacement results instantly. No signup, no install.
Live Matches
Capture Groups
i m s x Flags
Find & Replace
Regex Tester & Debugger
Enter pattern → paste test string → click Test Regex
Regex Syntax Cheatsheet
The most commonly used regular expression tokens with examples
| Token | Meaning | Example | Matches |
|---|---|---|---|
| . | Any character except newline | c.t | cat, cot, cut |
| \d | Any digit 0–9 | \d{4} | 2026, 1999 |
| \w | Word char [a-zA-Z0-9_] | \w+ | hello, user_1 |
| \s | Whitespace (space, tab, newline) | \s+ | Spaces between words |
| ^ | Start of string / line | ^Hello | Lines starting with Hello |
| $ | End of string / line | \d+$ | Numbers at end of line |
| * | Zero or more (greedy) | ab*c | ac, abc, abbc |
| + | One or more (greedy) | ab+c | abc, abbc (not ac) |
| ? | Zero or one (optional) | colou?r | color, colour |
| (…) | Capture group | (\d{4})-(\d{2}) | 2026-01, captures year+month |
| […] | Character class | [aeiou] | Any single vowel |
| | | Alternation (OR) | cat|dog | cat or dog |
Ready-to-Use Regex Patterns
Copy any pattern directly into the tester above
📧 Email Address
[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}🌐 URL / Web Address
https?:\/\/[^\s/$.?#].[^\s]*📱 US Phone Number
(\+1[-.\s]?)?\(?\d{3}\)?[-.\s]\d{3}[-.\s]\d{4}🎨 Hex Colour Code
#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})📅 ISO Date YYYY-MM-DD
\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])🔐 Strong Password
^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*])[A-Za-z\d@$!%*]{8,}🌍 IPv4 Address
(?:(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d\d?)🏷️ HTML Tag Stripper
<[^>]*>Regex Flags Explained
How each flag changes your pattern's behaviour
iCase InsensitiveMakes the pattern match both uppercase and lowercase letters. hello matches Hello, HELLO, hElLo.
mMultilineMakes ^ and $ match the start and end of each line, not just the whole string.
sDot AllMakes . match newline characters too. Without this flag, . does not match
.
xVerboseAllows whitespace and comments inside the pattern. Use # for inline comments in complex patterns.
Frequently Asked Questions
Common questions about regular expressions and this tool
What is a regular expression (regex)?
A regular expression is a sequence of characters that defines a search pattern. It is used to match, find, extract, replace, and validate strings. Regex is supported in Python, JavaScript, Java, PHP, Ruby, Go, and virtually every other language. Syntax varies slightly between Python re, JavaScript RegExp, and PCRE flavours.
What is the difference between greedy and lazy matching?
Greedy quantifiers (*, +, ?) match as much as possible. Lazy quantifiers (*?, +?, ??) match as little as possible. For example given <b>bold</b>, the greedy pattern <.*> matches the entire string, while the lazy <.*?> matches only <b>.
What are capture groups and backreferences?
Capture groups are defined with parentheses and extract specific portions of a match. Group 0 is the full match, group 1 is the first (…), etc. Named groups use (?P<name>…) syntax in Python. Backreferences (, ) reference captured groups within the same pattern or replacement string.
Does this tool use Python or JavaScript regex?
This tool uses Python's built-in re module on the server side. Python regex is largely compatible with PCRE but differs from JavaScript's RegExp — notably named groups use (?P<name>…) syntax. Flags i, m, s, and x are supported.
How do I match a literal dot or special character?
Escape special characters with a backslash: \. matches a literal dot, \( matches a literal parenthesis, \ matches a literal backslash. Special regex characters needing escape: . ^ $ * + ? { } [ ] | ( ) \
What does the i flag do and when should I use it?
The i (case insensitive) flag makes your pattern match regardless of letter case. With i, the pattern hello matches Hello, HELLO, and hElLo. Use it for case-agnostic matching in user input validation, search features, and log parsing.