Which regex flavor does this use?

It uses the JavaScript regular expression engine that runs in your browser. Patterns behave exactly as they would in JavaScript code, including support for flags like g, i, m, s, and u.

Why isn't my pattern matching anything?

Common causes are a missing flag (for example, no g flag so only the first match is found), an unescaped special character, or anchors like ^ and $ behaving differently without the multiline m flag. Try simplifying the pattern and adding pieces back.

How do I match across multiple lines?

Add the m flag so ^ and $ match at line boundaries, and the s flag if you want the dot to also match newline characters.

Do I need to escape special characters?

Yes. Characters like . * + ? ( ) [ ] { } ^ $ | and the backslash have special meaning in regex. Escape them with a backslash when you want to match them literally.

Is my test text sent anywhere?

No. Matching runs entirely in your browser, so neither your pattern nor your test string is uploaded or stored.

Regex Highlighter

Highlight matching text in real-time using your custom regular expressions.

Tool

Enter your Regex pattern, flags, and test string.

Regular Expression

//g

Flags

Global (g) - Find all matches

Case Insensitive (i)

Multiline (m) - ^ and $ match start/end of line

Dot All (s) - . matches newline characters

Unicode (u) - Treat pattern as sequence of Unicode points

Sticky (y) - Match only from index indicated by lastIndex

Test String

Result / Matches Highlighted

The quick brown fox jumps over the lazy dog.

About Regex Highlighter

Writing a regular expression is easy; knowing exactly what it matches is the hard part. A pattern that looks correct can quietly miss edge cases, match too greedily, or fail on the one input that matters. The fastest way to build confidence is to see the matches highlighted against real text as you type.

This tool takes your pattern, your flags, and a test string, and paints every match directly onto the input. Change a quantifier, add a flag, or paste a different sample and the highlights update instantly — so you can tune the expression until it captures exactly what you intend and nothing more.

Everything runs in your browser using the native JavaScript regex engine, so the matches you see are the matches your code will get. No text is uploaded or stored, which makes it safe to test patterns against logs, config snippets, or anything else you'd rather keep local.

How to use Regex Highlighter

Enter your pattern
Type the regular expression you want to test into the pattern field — just the body, without the surrounding slashes.
Set the flags
Add flags such as g (global), i (case-insensitive), or m (multiline) to control how the pattern is applied.
Paste your test string
Drop in the sample text you want to match against — a log line, a list of values, or any block of content.
Read the highlights
Matches are highlighted in place as you type. Refine the pattern until only the text you want is highlighted.

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