Java Regex Tester

• Copyable Pattern.compile / Matcher code with backslashes pre-doubled ("\\d+")
• String.matches() anchors the WHOLE string; Matcher.find() scans — the #1 Java regex confusion
• Named groups (?<name>…) supported since Java 7 — read with matcher.group("name")
• Flags: Pattern.CASE_INSENSITIVE etc., or inline (?i)(?m)(?s) prefixes
• Java 13+ text blocks or Pattern.quote() reduce escaping pain for literals

Frequently Asked Questions

Why does my pattern work here but String.matches() returns false?

Because matches() requires the pattern to consume the ENTIRE string — it wraps your pattern in implicit \A…\z anchors. If the pattern matches a substring (what this tester highlights), use Matcher.find() instead: Pattern.compile(re).matcher(s).find(). Use matches() only for whole-input validation.

Why do Java regex strings need double backslashes?

Java string literals process escapes first: "\d" is an invalid string escape, so the regex \d must be written "\\d" — one backslash for the string parser, one for the regex engine. The Java snippet this page generates doubles them automatically. To match a literal backslash you need four: "\\\\".

How do I get all matches in Java (the g flag)?

Loop with find(): Matcher m = pattern.matcher(input); while (m.find()) { m.group(); }. Java 9+ adds m.results() for a Stream<MatchResult>, and String.split / pattern.splitAsStream cover the splitting cases.

Does Java support lookbehind and named groups?

Yes — java.util.regex supports lookahead, lookbehind (including variable-width in modern JDKs, unlike Python), named groups (?<name>…) since Java 7 via matcher.group("name"), and possessive quantifiers (a++) that JavaScript lacks. Patterns tested here transfer cleanly; just double the backslashes.

Is this tester free and private?

Yes — free, no signup, no limits, and 100% client-side: patterns and test strings are processed in your browser and never sent to a server.