Regex Tester

About regex testing

Regular expressions are the standard tool for validating input, extracting substrings, and rewriting text — and the fastest way to get them right is to iterate live against real samples. This tester runs JavaScript's native RegExpengine in your browser: type a pattern, watch matches highlight as you type, inspect capture groups, and flip to replace mode to see a rewrite applied.

Flag reference

The checkboxes toggle JavaScript's standard RegExp flags:

gglobal —

finds every occurrence in the text. Without it, replace mode only rewrites the first match.

iignore case —

letter case no longer matters — /hello/i matches "Hello" and "HELLO".

mmultiline —

the ^ and $ anchors match at the start/end of every line, not just the whole string.

sdot all —

the dot also matches newline characters, so patterns like .+ can span multiple lines.

uunicode —

full Unicode semantics — emoji and other astral characters are treated as single characters, and \u{1F600}-style code point escapes work.

ysticky —

matches are anchored to the exact current position (lastIndex) — mainly useful for tokenizers.

Zero-width matches

A pattern like a* can match an empty string, which on many sites makes a regex tester hang or flood the page with zero-width results. This tool advances past zero-width matches automatically and skips them in the highlight, so you can experiment freely with quantifiers like* and ?.

Related tools

Validate the result against structured data with the JSON formatter, or build a reusable config in the JSON to YAMLconverter.