Is this PCRE or JavaScript regex syntax?

It uses the browser's native JavaScript RegExp engine. Features and edge cases may differ from PCRE, Python, Java, .NET and older browsers.

What does the Global flag affect?

With g enabled, matching and replacement continue through all applicable results. Without it, native JavaScript stops after the first match.

Are named capture groups shown?

Yes, when the pattern and browser support them. Numbered captures, unmatched optional groups and match start and end indexes are also reported.

How are zero-length matches handled?

The evaluator advances safely after an empty global match to prevent an infinite loop while retaining the genuine match location.

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Regular Expression Tester

Exercise native JavaScript patterns against multiline text with safe match highlighting, capture details and replacement previews.

Regular Expression

Test String

Match Preview

Enter a regular expression to begin.

Match Details

Match details will appear after a valid pattern and test string are available.

Replace

Enter a pattern and test string to view the replacement result.

Quick Reference

.: Any character
\d: Digit
\D: Non-digit
\w: Word character
\W: Non-word character
\s: Whitespace
\S: Non-whitespace
^: Start
$: End
\b: Word boundary
*: Zero or more
+: One or more
?: Zero or one
{n}: Exactly n
{n,m}: Between n and m
[abc]: Character set
[^abc]: Negated character set
(...): Capture group
(?:...): Non-capturing group
(?<name>...): Named capture group
a|b: Alternation

Your regular expression and test data are processed locally in your browser.

How to use Regular Expression Tester

1
Enter a JavaScript regular expression without surrounding slash delimiters, or load the sample.
2
Enable any Global, Ignore case, Multiline, Dot all, Unicode or Sticky flags required.
3
Paste the Test String and inspect live highlights plus the match count.
4
Open Match Details to review indexes, numbered captures and named capture groups.
5
Enter replacement text with JavaScript references and copy the previewed result if needed.

Frequently asked questions

About Regular Expression Tester

Regular expressions are easiest to debug when the engine is explicit. This tester compiles patterns with the browser's JavaScript RegExp implementation and surfaces syntax failures separately from an ordinary zero-match result. Six standard flags can be combined without wrapping the pattern in slash notation.

Highlights are rendered as safe text, while the detail list records exact indexes and every capture. A companion replacement preview follows native JavaScript substitution rules, including complete-match, numbered and named references. Nothing is submitted to an external regex service.