Which named group syntaxes are supported?

The tester supports Python-style (?P ...), Perl/Oniguruma style (? ...), and single-quoted (?'name'...) formats, along with corresponding backreferences.

How are atomic groups and possessive quantifiers evaluated?

They are translated using lookahead-capture mechanisms within the engine to prevent backtracking, replicating PCRE2 execution semantics.

Does \d match all Unicode digits by default?

No. By default, \d, \w, and \s maintain ASCII-only PCRE2 semantics unless the Unicode character classes option is checked.

What happens if I use an unsupported PCRE2 construct?

Constructs that cannot be evaluated accurately—such as recursion ((?R)), callouts, \K, \G, or backtracking control verbs—are detected and rejected with an explanatory message.

Can this tool preview regular expression replacements?

Yes, entering a pattern into the optional replacement template field provides a live preview of the substituted output using capture references.

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PCRE2 Regex Tester

Test PCRE2 patterns online: every named-group syntax ((?P<n>), (?<n>), (\u0027n\u0027)), possessive quantifiers, atomic groups, \A \z \h shorthands, plus pcre2grep and C API snippets.

Details

What this tool helps you do

A regex tester for the PCRE2 flavor (PHP preg*, pcre2grep, Delphi, R, and many tools). PCRE2 accepts every named-group syntax — (?P…), (?…), (?\u0027year\u0027…) — with backreferences \k, \k{year}, \g{year} and (?P=year); the tester accepts all of them, translates to the platform\u0027s ECMAScript engine, and reports matches, named capture groups, and a replace preview. Shorthands missing from JavaScript are expanded: \A and \z absolute anchors, \Z end-before-final-newline, \h / \H horizontal whitespace. Possessive quantifiers and atomic groups are emulated with lookahead-capture so they really prevent backtracking, and ASCII \d \w \s semantics stay PCRE2-default (toggle Unicode classes to emulate PCRE2UCP). Constructs the ECMAScript engine cannot express — recursion ((?R), (?1)), conditionals ((?(1)…)), callouts (?C…), \K, \G, backtracking verbs — are detected and rejected with an explanation. The report also builds pcre2grep command lines and a pcre2compile / pcre2match C API sketch.

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PCRE2 Regex Tester

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Use cases

Examples

1. Log parsing with start-of-string anchor and named groups

2. Horizontal whitespace and atomic token matching

FAQ

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