What is a Regex Tester?

A Regex Tester is an online tool that allows you to write a Regular Expression (RegExp) pattern and test it against a block of text in real-time. It helps you debug your pattern and see exactly what it matches (and what it doesn't).

What do the regex flags 'g', 'i', and 'm' mean?

Flags modify the search behavior: g (global) finds all matches, not just the first. i (case-insensitive) makes the pattern ignore case (e.g., 'a' matches 'a' and 'A'). m (multi-line) allows the start (^) and end ($) anchors to match the start and end of individual lines, not just the whole string.

Is this a JavaScript Regex Tester?

Yes. This tool uses your browser's built-in JavaScript RegExp engine to perform the test. This means the syntax and behavior (including flags and lookaheads) are exactly what you would expect in your JavaScript code.

Regex Tester & Validator

Test & debug JavaScript regular expressions (RegExp) in real-time.

100% Client-Side & Secure

All Regex validation and testing happens in your browser.
Your expressions and test strings are never stored or sent to our servers.
It's safe to use with sensitive logs or data.

What is a Regular Expression (Regex)?

A Regular Expression (or RegExp) is a powerful sequence of characters that defines a search pattern. It's a "mini-language" used to find, match, validate, or replace text within strings.

Instead of searching for a fixed word like "email", you can create a pattern that matches *any* email address. This tool is an online regex tester that lets you build and debug these complex patterns in real-time.

Key Use Cases:

Validation: Check if user input is valid (e.g., "is this a valid email?", "is this a strong password?").
Find & Replace: Perform advanced text replacement (e.g., find all http:// links and change them to https://).
Data Parsing: Extract specific pieces of information from large blocks of text, like log files or HTML.

This tool uses the JavaScript RegExp engine, so your patterns will behave exactly as they would in your web application.

Regex Examples

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Regex Best Practices & Key Concepts

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Escape Special Characters

Characters like ., +, *, ?, (, ), [, ], {, }, and \ have special meanings in regex. To match them as literal characters, you must escape them with a backslash (\). For example, to find a literal dot, use \..

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Greedy vs. Lazy Matching

By default, quantifiers like * and + are "greedy"—they match as *much* text as possible. To make them "lazy" (match as *little* text as possible), add a ?. For example, <.*> will match from the first < to the last >. <.*?> will match each HTML tag individually.

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What 'g', 'i', 'm' Flags Mean

Flags are added after the final / to change the search:
g (global): Finds all matches, not just the first one.
i (case-insensitive): Ignores case (e.g., /a/i matches 'a' and 'A').
m (multi-line): Allows anchors (^, $) to match the start/end of lines, not just the whole string.