Does this highlight all matches or just the first one?

All matches, by default. The tool always applies the global flag internally (adding it automatically if you don't include it in your flags), so every occurrence in the text is wrapped.

Can I use a custom marker instead of asterisks?

Yes, the marker field accepts any string, such as '**', '[[', ' >' or emoji; it's placed on both sides of every match.

What happens with an invalid pattern?

The tool reports the JavaScript RegExp error message rather than silently failing, so you can see exactly what's wrong with the pattern.

Regex Match Highlighter - Wrap Matches with Markers

Overview

Introduction

When developing or debugging a regular expression, it helps to see exactly which parts of a text it matches, right in place.

This tool runs entirely client-side, so nothing you paste is ever uploaded to a server.

What Is RegExp Match Highlighter?

A regex tool that wraps every match of a pattern in your text with a marker string on both sides, so matches stand out visually without leaving the plain-text format.

It's part of this site's String Tools collection and works entirely in your browser, updating the highlighted output as you type.

How RegExp Match Highlighter Works

The tool compiles your pattern and flags into a JavaScript RegExp, automatically ensuring the global flag is included so every match (not just the first) is found.

It then uses `String.prototype.replace()` to wrap each matched substring with your chosen marker string on both the left and right side.

When To Use RegExp Match Highlighter

Use it while building or debugging a regular expression, to confirm exactly which substrings it matches in a sample text.

It's also handy for annotating a plain-text document to flag specific patterns, such as all-caps words or dates, without special formatting.

Often used alongside Regex Tester and Regex Match Extractor.

Features

Advantages

Automatically forces the global flag so you always see every match, not just the first.
Custom marker string works in any plain-text context, including places that don't support rich highlighting.
Leaves the surrounding text in place, so every match is visible in context rather than pulled out into a separate list.

Limitations

Output is plain text with markers inserted; it does not render actual visual highlighting or color.
Uses the same marker on both sides, so two matches sitting next to each other can be hard to tell apart.

Examples

Highlighting digit sequences

Input

pattern="\\d+", text="Room 12 has 4 chairs"

Output

Room **12** has **4** chairs

With the default marker '**', every run of digits in the text is wrapped on both sides.

Best Practices & Notes

Best Practices

Use a marker unlikely to appear naturally in your text, so wrapped matches are easy to distinguish from the surrounding content.
Try the pattern on a short excerpt first, since a broad pattern can wrap almost the whole text and hide what you were looking for.
Avoid patterns capable of matching an empty string, which insert markers between every single character.

Developer Notes

Flags are normalized with `flags.includes("g") ? flags : flags + "g"` before constructing the RegExp, guaranteeing every match is replaced via `input.replace(regex, (match) => \`${marker}${match}${marker}\`)`.

RegExp Match Highlighter Use Cases

Verifying a regex pattern matches the expected substrings
Annotating plain text to flag matches for a teammate
Building a quick before/after example of a regex pattern's effect

Common Mistakes

Forgetting that markers are inserted as literal text, not HTML or Markdown formatting.
Using a marker string that also appears in the text, making wrapped and unwrapped occurrences hard to tell apart.

Tips

Try a distinctive marker like '<<' and '>>' style pairs when your text already contains asterisks or other common symbols.
Use the Regex Match Extractor when you want the matches as a list, and this tool when their position within the text is what matters.

RegExp Match Highlighter