What regex flavor does this tester use?

This tool uses JavaScript's native RegExp engine, the same one used in browser JavaScript and Node.js. Syntax may differ slightly from other flavors like PCRE (used in PHP) or Python's re module.

What is the difference between the g, i, m, s, and u flags?

The g flag finds all matches instead of stopping at the first one. The i flag makes matching case-insensitive. The m flag makes ^ and $ match the start and end of each line instead of the whole string. The s flag lets . match newline characters. The u flag enables full Unicode-aware matching.

How do I reference capture groups in the replacement text?

Use $1, $2, and so on to reference numbered capture groups from your pattern in the replacement field. For named capture groups defined with (? ...), use $ in the replacement instead.

Why does my regex throw a syntax error?

This usually happens due to unescaped special characters, mismatched brackets or parentheses, or invalid flag combinations. Common issues include forgetting to escape characters like . ( ) [ ] when they should be treated literally.

Can I test multiline text with this regex tester?

Yes, paste multiline text into the test area and enable the m (multiline) flag if you want ^ and $ to match the start and end of individual lines rather than the entire text block.

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Pattern & Test Text

0 characters

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

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Highlighted Matches

0 matches

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Match Details

Capture groups included

Status

No regex tested yet.

`matchAll()` is useful for collecting all matches and capture groups, but it requires a regex with the global `g` flag when used directly with a `RegExp` object.

How it works

JavaScript uses the `RegExp` object for pattern matching, and tools like this typically build a regex from a user pattern plus selected flags such as `g`, `i`, `m`, `s`, and `u`. To inspect every match and its captured groups, `String.prototype.matchAll()` is especially convenient, but it requires a global regex when passed a `RegExp` instance.

g finds all matches, not just the first one.
i makes matching case-insensitive.
m makes `^` and `$` work per line in multiline text.
s makes `.` match newline characters too.
u improves Unicode handling in JavaScript regex parsing and matching.

Common regex patterns

Use case	Pattern
Email address	^[\w.+-]+@[\w-]+\.[a-zA-Z]{2,}$
Indian mobile number	^[6-9]\d{9}$
URL	^https?:\/\/[\w.-]+(\.[a-zA-Z]{2,})+[\S]*$
Hex color code	^#([0-9a-fA-F]{3}\|[0-9a-fA-F]{6})$
Date (YYYY-MM-DD)	^\d{4}-\d{2}-\d{2}$

Frequently Asked Questions

This tool uses JavaScript's native RegExp engine, the same one used in browsers and Node.js. Syntax may differ slightly from PCRE (PHP) or Python's re module.

g finds all matches instead of just the first. i makes matching case-insensitive. m makes ^ and $ match per line. s lets . match newlines. u enables full Unicode-aware matching.

In JavaScript, String.replace() only replaces the first match unless the regex has the global (g) flag enabled. Check the g checkbox to replace all matches.

Use $1, $2, and so on for numbered capture groups. For named groups defined with (?<name>...), use $<name> in the replacement instead.

Usually caused by unescaped special characters, mismatched brackets or parentheses, or invalid flag combinations. Remember to escape characters like . ( ) [ ] when treating them literally.

Yes, paste multiline text into the test area and enable the m (multiline) flag if you want ^ and $ to match line boundaries rather than the whole text block.

Regex Tester