Developer Tool Developer Tool

Regex Tester

Build, test, debug, and replace text with PCRE-compatible regular expressions.

✓Live matches ✓Capture groups ✓Replacement preview

Pattern

//g

Test text Replacement

5 matches found.

Matches

5 Matches

HelloOffset 0

BuildOffset 21

BetterOffset 27

DeveloperOffset 34

ToolsOffset 44

Replacement Preview

[Hello] from ToolNest.
[Build] [Better] [Developer] [Tools].

How to Use

Enter a pattern without delimiters, choose flags, paste test text, and inspect every match, offset, capture group, and replacement result.

Supported Flags

g: Global
i: Ignore case
m: Multiline anchors
s: Dot matches newline
u: Unicode mode

Test expressions before shipping them

Regex behavior depends on flags, anchors, greediness, and capture groups. Validate representative inputs and edge cases before using a pattern in validation or data processing.

Frequently Asked Questions

Which regex flavor is used? +

The tester uses PHP PCRE syntax. Enter the pattern without surrounding delimiters.

How do capture groups work? +

Parenthesized subpatterns appear beneath each full match.

What does global mean? +

Global mode returns every non-overlapping match instead of only the first.

Is catastrophic backtracking possible? +

Poorly designed patterns can be expensive; keep patterns and test data bounded.

Regex Quantifiers Greedy and lazy matching Capture Groups Extract structured values Regex Performance Avoid backtracking traps

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