Advanced Regex Tester Online – Free Real-Time Regex Debugger & Builder

GHOSTOOLS · DEVELOPER UTILITIES

Advanced Regex Tester

Build, test, debug, and understand regular expressions in real time. Inspect matches, capture groups, match positions, and replacement results — free, right in your browser.

Regex Playground

Regular expression

Regex engine

Ready. Edit the pattern or test string to update results automatically.

Test String

Enter your test text

Hello Ghostools!
Regex makes text processing easier.
Contact: hello@example.com
Website: https://www.example.com

Live Results

0Matches

0Capture groups

0Input characters

Match Highlighting Waiting

Your highlighted text will appear here.

Match Details 0 results

Enter a valid pattern to inspect matches and capture groups.

Find & Replace

Test a replacement string using JavaScript replacement syntax, including $&, $1, and $$.

Replacement string

Replacement Preview Not run

Your replacement result will appear here.

Regex Pattern Library

Select a pattern to load it into the playground. Examples use JavaScript-compatible regular expressions.

Quick Regex Reference

.Matches any character except line terminators, unless the s flag is enabled.

\\dMatches an ASCII digit from 0 to 9.

\\wMatches ASCII letters, digits, and underscore in standard JavaScript regex mode.

\\sMatches whitespace characters.

^ $Match string boundaries, or line boundaries with the m flag.

* + ?Quantifiers: zero or more, one or more, and optional.

{n,m}Matches a repetition count within the specified range.

[abc]Matches any one character from the specified character set.

(abc)Capturing group. Use (?:abc) for a non-capturing group.

(?=abc)Positive lookahead. Checks what follows without consuming it.

(?!abc)Negative lookahead. Checks that a pattern does not follow.

|Alternation: matches the expression on either side.

\\bWord boundary based on JavaScript's word-character rules.

g i m s u y dGlobal, ignore case, multiline, dotAll, Unicode, sticky, and match indices.

This tool uses the browser's native JavaScript regular-expression engine. It does not implement PCRE, Python, .NET, or every feature available in other regex engines.

Frequently Asked Questions

What is an online regex tester?

A regex tester lets you write a regular expression, test it against sample text, inspect matches and capture groups, and preview replacements without setting up a development environment.

What regex engine does this tool use?

This tool uses the native JavaScript RegExp engine available in your browser. Syntax and supported features may differ from Python, PCRE, Java, or .NET.

What do the global and multiline flags do?

The global flag finds successive matches throughout the input. The multiline flag makes the start and end anchors operate at individual line boundaries.

Is my text sent to a server?

The regex matching, highlighting, and replacement operations run locally in your browser. This tool does not intentionally upload your test text to a server.

Why is my regular expression invalid?

Check for missing parentheses, unclosed character classes, invalid escape sequences, unsupported syntax, or incompatible flags. Named groups and other advanced syntax depend on browser support.

Can this tool prevent catastrophic regex backtracking?

No. JavaScript regex evaluation is synchronous, and some patterns can consume excessive processing time on certain inputs. Avoid testing untrusted patterns or very large inputs with ambiguous nested quantifiers.