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Regex Tester

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

Live matchesCapture groupsReplacement preview

5 matches found.

Matches

5 Matches
HelloOffset 0
BuildOffset 27
BetterOffset 33
DeveloperOffset 40
ToolsOffset 50

Replacement Preview

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

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.

What is Regex Tester?

Regex Tester evaluates a PCRE pattern against sample text and displays full matches, offsets, capture groups, and replacement output. It gives developers and data teams a contained place to refine extraction or validation logic before placing a pattern in application code.

How to use Regex Tester

  1. 1.Enter the pattern without surrounding delimiter characters.
  2. 2.Enable only the flags required for case, multiline, dot-all, Unicode, or global behavior.
  3. 3.Paste representative text and inspect each match and capture group.
  4. 4.Try replacement syntax where needed, then copy the tested pattern into code with the correct language escaping.

Key features

  • ✓PCRE-compatible matching reflects common PHP regular-expression behavior.
  • ✓Match offsets show exactly where each result begins in the test string.
  • ✓Capture-group output distinguishes the complete match from extracted subpatterns.
  • ✓Replacement preview tests backreferences before implementation.
  • ✓Bounded input and clear errors help diagnose invalid patterns or flags.

Common use cases

  • Extract order numbers from a batch of support messages.
  • Test a log-line parser before adding it to an import job.
  • Validate the shape of a controlled identifier rather than unrestricted user prose.
  • Preview a search-and-replace rule for cleaning exported text.

Frequently asked questions

Which regular expression flavor does this tester use?

It uses PHP PCRE-style syntax. Patterns written for JavaScript, Python, or another engine may require changes.

Should I include slash delimiters around the regex?

No. Enter only the pattern because the tool supplies safe delimiters internally.

How can I see every regex match instead of the first?

Enable global matching to return all non-overlapping results in the sample text.

Why is my regex slow on a long string?

Nested ambiguous quantifiers can cause excessive backtracking. Simplify the pattern, add boundaries, and test it against realistic maximum input sizes.

Can regex reliably validate an email address?

A practical pattern can reject obvious mistakes, but complete address rules are complex. Confirmation email is more dependable than an extremely strict regex.

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