What's the difference between $1, ${1} and $ in the replacement?

All three reference capture groups. `$1` and `${1}` refer to the first un-named capture group. `$ ` refers to a named group declared with `(? ...)`. JavaScript supports `$&` (whole match) and `$$` (literal dollar sign).

Developer Tool

Regex Tester & Cheatsheet

Test JavaScript and PCRE regex live — see matches, capture groups, replacement preview, flag toggles. Plus full cheatsheet and pattern library. No signup, no ads.

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Quick Answer

The Regex Tester compiles your JavaScript regular expression live, highlights every match in your test string, displays each capture group, and previews a substitution result — with a full cheatsheet, 7 common-pattern presets and detailed error messages. 100% client-side, no paywall.

Test string

Highlighted matches (0)

Jane Doe met John Smith at the FreeAIToolz HQ. Mary Sue joined later.

Replace / substitution

Regex cheatsheet

\dAny digit (0–9)

\wWord character (a–z, A–Z, 0–9, _)

\sWhitespace

.Any character except newline

^Start of line

$End of line

\bWord boundary

[abc]Character class — a, b, or c

[^abc]Negated class — NOT a, b, or c

a|bAlternation — a OR b

a*0 or more of a

a+1 or more of a

a?0 or 1 of a (optional)

a{2,4}Between 2 and 4 of a

(abc)Capture group

(?:abc)Non-capture group

(?<name>abc)Named capture group

(?=abc)Positive lookahead

(?!abc)Negative lookahead

Quick Facts

Tool Name: Regex Tester & Cheatsheet
Category: Developer Tool
Price: Free browser utility; device and input limits apply.
Platform: Browser Based
Login Required: ✓ No
Processing & privacy: The core calculation runs in your browser. This tool does not need a paid AI API for its core output.
Scope: Results describe the submitted input and supported checks. They do not guarantee accuracy, search rankings, indexing or AI citations. Read our testing and scoring methodology.

How to Use Regex Tester & Cheatsheet

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Frequently Asked Questions

Everything you need to know about Regex Tester & Cheatsheet

Which regex flavor does this support?

JavaScript regex (ECMAScript) — the same flavor used by Node.js, V8 (Chrome) and SpiderMonkey (Firefox). Most patterns also work in PCRE, Python re, Go regexp and Ruby. The cheatsheet flags any token that isn't portable.

What do the flags g, i, m, s, u, y do?

`g` = global (find all matches, not just first). `i` = case-insensitive. `m` = multiline (`^` and `$` match each line). `s` = dotAll (`.` matches newlines too). `u` = unicode (correctly handles surrogate pairs). `y` = sticky (match starts at lastIndex).

Why does the tool stop after 500 matches?

Browser performance — beyond 500 matches the highlighter slows the page. If you need to extract every match from huge text, paste a smaller chunk or use the pattern in Node.js / Python locally.

Are my pattern and text uploaded to a server?

No. The entire tester — including the substitution preview and capture-group display — runs in your browser via the native `RegExp` object. Nothing is logged.

What's the difference between $1, ${1} and $<name> in the replacement?

All three reference capture groups. `$1` and `${1}` refer to the first un-named capture group. `$<name>` refers to a named group declared with `(?<name>...)`. JavaScript supports `$&` (whole match) and `$$` (literal dollar sign).

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