Regex Tester & Builder (JavaScript)
Pattern, Flags & Text
Tip: Ctrl/Cmd + K focuses the pattern. Ctrl/Cmd + Enter tests.
Results
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Matches & Groups
Shows match index, ranges, and capture groups (group ranges require d if supported).
Note: This uses your browser’s ECMAScript regex engine. Some PCRE tokens (e.g., atomic groups) aren’t supported.
Understanding Regular Expressions
A Regular Expression (Regex) is a pattern for matching text. Use them to search, validate, and replace.
Common examples
- Email:
^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$ - IPv4:
^((25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(25[0-5]|2[0-4]\d|[01]?\d\d?)$ - ISO date (YYYY-MM-DD):
^\d{4}-\d{2}-\d{2}$
Character classes
. any char · \w/\d/\s word/digit/space · [a-z] ranges
Anchors
^ start · $ end · \b word boundary
Groups & lookaround
(…) capture · (?:…) non-capture · (?=…)/(?!…) lookahead
Quantifiers
*/+/? · {m,n} · +? lazy