RegEx Tester

Test and debug regular expressions

Regular Expression

Flags

g (global) i (ignore case) m (multiline) s (dotAll)

Test String

Matches

No matches found

Highlighted Result

Common Patterns

What are Regular Expressions?

Regular expressions (regex or regexp) are patterns used to match character combinations in strings. They're an incredibly powerful tool for searching, validating, extracting, and replacing text. Originally developed in the 1950s, regex is now supported in virtually every programming language and text editor.

This tool uses JavaScript's regex engine, which implements the ECMAScript standard. Test your patterns here before using them in your code—all processing happens in your browser with no data sent to servers.

Regex Syntax Quick Reference

Character Classes

\d - Any digit (0-9)
\w - Word character (a-z, A-Z, 0-9, _)
\s - Whitespace (space, tab, newline)
. - Any character except newline
[abc] - Any of a, b, or c
[^abc] - Not a, b, or c

Quantifiers

* - 0 or more
+ - 1 or more
? - 0 or 1 (optional)
{n} - Exactly n times
{n,} - n or more times
{n,m} - Between n and m times

Anchors & Boundaries

^ - Start of string/line
$ - End of string/line
\b - Word boundary
\B - Non-word boundary

Groups & Alternation

(abc) - Capture group
(?:abc) - Non-capture group
a|b - Either a or b
\1 - Backreference to group 1

Understanding Flags

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

i (ignore case) - Case-insensitive matching (A matches a)

m (multiline) - ^ and $ match start/end of each line, not just the string

s (dotAll) - Makes . match newline characters too

Frequently Asked Questions

Why do I need to escape backslashes?

In JavaScript strings, backslash is an escape character. To include a literal backslash in a regex pattern from a string, you need \\. For example, \\d in a string becomes \d in the regex.

What's the difference between * and +?

* matches zero or more occurrences (can match nothing). + requires at least one occurrence. For example, a* matches "", "a", "aaa", while a+ only matches "a", "aaa".

How do I match a literal period or bracket?

Special regex characters need to be escaped with a backslash. To match a literal period, use \.. For brackets: \[ and \]. Characters that need escaping: . * + ? ^ $ { } [ ] \ | ( )

Why is my pattern matching too much?

Regex quantifiers are "greedy" by default—they match as much as possible. Add ? after a quantifier for "lazy" matching (e.g., .*? instead of .*).

Common Use Cases

Form Validation: Validate emails, phone numbers, URLs, and custom formats
Search & Replace: Find and transform text patterns in editors and code
Log Parsing: Extract timestamps, IPs, and error codes from log files
Data Extraction: Pull specific data from HTML, JSON, or unstructured text
Input Sanitization: Remove or escape dangerous characters