Regular Expression Tester
Write your regex pattern, pick flags, and see matches highlighted live over your test text, with a list of matches and captured groups.
Expression and flags
/…/g
Test text
How to use: Regex
- 1Type the regular expression and toggle flags (g, i, m, s, u).
- 2Paste the test text.
- 3Review the highlighted matches and captured groups.
What is it for?
- Validate emails, phone numbers or postal codes.
- Test search-and-replace patterns before using them in code.
- Extract data from logs or long texts.
Regular expressions without surprises
Basic building blocks
\d matches a digit, \w a letter, digit or underscore and \s a whitespace character. The quantifiers *, + and ? mean "zero or more", "one or more" and "optional"; {n,m} sets a range. ^ and $ anchor to the start and end, and parentheses form groups you can capture and reuse.
Greedy versus lazy
By default quantifiers are greedy: they try to match as much as possible. In <.+> applied to "<a><b>" it captures the whole string; with <.+?> it captures each tag separately. Many "it captures too much" bugs are solved with the lazy version or a negated class such as [^>]+.
Flags
g finds all matches, i ignores case, m makes ^ and $ work per line, s lets the dot match line breaks and u enables Unicode mode, needed for emoji and characters outside the basic plane. This tool uses the JavaScript regular expression engine.
Performance and security
Patterns with nested quantifiers such as (a+)+ can cause catastrophic backtracking (ReDoS) on certain inputs and freeze a process. If you validate user text on a server, avoid such constructs and cap the input length.
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Frequently asked questions
Which regex engine does it use?+
The ECMAScript (JavaScript) engine, the same one browsers and Node.js use.