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RegexBuilder

Regex Tester

Test JavaScript regular expressions with live match highlighting, replace mode, and a pattern library.

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Regex Quick Reference
Character Classes
.Any character except newline
\dDigit [0-9]
\DNon-digit
\wWord char [a-zA-Z0-9_]
\WNon-word character
\sWhitespace
[abc]Character set
[^abc]Negated set
[a-z]Range
Anchors
^Start of string/line
$End of string/line
\bWord boundary
\BNon-word boundary
Quantifiers
*0 or more (greedy)
+1 or more (greedy)
?0 or 1 (optional)
{n}Exactly n times
{n,m}Between n and m times
*?0 or more (lazy)
Groups & Alternation
(abc)Capture group
(?:abc)Non-capturing group
a|bAlternation (a or b)
(?=abc)Positive lookahead
(?!abc)Negative lookahead
\1Backreference to group 1

Regular expression basics

A regular expression (regex) is a sequence of characters that defines a search pattern. This tester uses JavaScript's native RegExp engine, which follows the ECMAScript specification.

  • . — matches any character except newline (use s flag for newlines).
  • * / + / ? — 0+, 1+, or 0–1 repetitions. Add ? after for non-greedy (*?, +?).
  • {n,m} — matches between n and m repetitions.
  • ^ / $ — start / end of string (or line with m flag).
  • [abc] / [^abc] — character class / negated character class.
  • (…) — capturing group. (?:…) is non-capturing.
  • \d \w \s — digit, word character, whitespace. Uppercase negates.
  • \b — word boundary.

Regex flags

  • g (global) — find all matches, not just the first.
  • i (case insensitive) — A matches a.
  • m (multiline) — ^ and $ match the start/end of each line, not just the whole string.
  • s (dot-all) — . matches newline characters as well.
  • u (unicode) — treat the pattern as a sequence of Unicode code points.

Using Replace mode

Switch to the Replace tab to preview substitutions live. The replacement string supports JavaScript's String.prototype.replace() syntax:

  • $1, $2, … — insert the text of capture group 1, 2, …
  • $& — insert the entire matched substring.
  • $` — insert the string before the match.
  • $' — insert the string after the match.
  • $$ — insert a literal $.

With the g flag enabled all occurrences are replaced; without it only the first match is substituted.

Common regex patterns

  • Email (basic) [a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}
  • URL https?://[^\s/$.?#].[^\s]*
  • IPv4 \b(?:\d{1,3}\.){3}\d{1,3}\b
  • Hex color #(?:[0-9a-fA-F]{3}){1,2}
  • ISO date \d{4}-\d{2}-\d{2}
  • Integer -?\d+
  • Decimal -?\d+(?:\.\d+)?
  • Whitespace trim ^\s+|\s+$