What is a regular expression (regex)?

A regular expression is a sequence of characters that defines a search pattern. Regex is used in programming, text editors, and command-line tools to find, match, replace, and validate text patterns. Common uses include email validation, log parsing, data extraction, and search-and-replace operations.

What regex flags are supported?

This tool supports all standard JavaScript regex flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), and u (unicode — enable full unicode support).

What are capture groups?

Capture groups are parts of a regex enclosed in parentheses (). They capture the matched text for later reference. Named capture groups use the syntax (? ...) and make extracted data easier to identify. This tool displays all capture groups with their values for each match.

Regex Tester

Test JavaScript regular expressions with real-time matching, capture groups, and highlighted preview. 100% client-side — nothing leaves your browser.

Pattern

/ /

Global (g) Case-insensitive (i) Multiline (m) DotAll (s)

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Frequently Asked Questions

A regular expression (regex) is a pattern that describes a set of strings. It's used in virtually every programming language for text search, validation, extraction, and replacement. For example, \d{3}-\d{4} matches phone numbers like 555-1234.

This tool uses your browser's native JavaScript regex engine (ECMAScript). Most patterns are compatible across languages, but some features like lookbehinds may vary. It supports named capture groups (?<name>...), lookaheads, and all standard flags.

Security analysts frequently use regex for IOC extraction: IP addresses (\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b), email addresses ([\w.-]+@[\w.-]+\.\w+), URLs (https?://[^\s]+), MD5 hashes (\b[a-fA-F0-9]{32}\b), SHA-256 hashes (\b[a-fA-F0-9]{64}\b), and domain names.

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Regex Tester

Test string

Matches

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Frequently Asked Questions

Navigation

Test string

Matches

Highlighted preview

Frequently Asked Questions

What is a regular expression?

What regex flavour does this tool use?

Common regex patterns for security analysts