Java Regex Tester

What is Java Regex Tester

Written by Giorgos Kostas. Last reviewed: April 18, 2026

Java Regex Tester evaluates Java-flavoured regular expressions against a sample string. Pattern goes on line 1, test text on the remaining lines. Matches, their positions, and captured groups are listed for quick debugging.

The underlying engine is the browser's RegExp, which covers the 95% of Java regex semantics (character classes, quantifiers, alternation, groups, named groups, lookahead) — with a note about the edge cases Java supports natively (possessive quantifiers, \A, \Z, wider lookbehind).

Why use it

• Debug regex patterns before pasting into Java code.
• Learn regex syntax with live feedback.
• Validate log-parsing patterns without launching a JVM.
• Prototype patterns for JUnit test assertions.
• Share reproducible regex snippets with teammates.

Features

• ECMAScript-equivalent Java regex testing
• Match positions and group capture
• Supports flags g/i/m/s/u/y
• Caps output at 1000 matches
• Processes Java Regex locally in your browser, no upload required

How to use Java Regex Tester

1. Write pattern on line 1. e.g. \b\w+@\w+\.\w+\b
2. Paste test text below. Add one or more lines to match.
3. Run. Review matches, positions, and groups.

Example (before/after)

\b(\w+)@(\w+\.\w+)\b
Reach us at [email protected] and [email protected]

Java regex (ECMAScript-equivalent): /\b(\w+)@(\w+\.\w+)\b/g
Test text: 52 chars

[0] "[email protected]" at 12 groups: [support, example.com]
[1] "[email protected]" at 36 groups: [sales, example.co]

Note: Java regex supports a few features (possessive quantifiers, \A, \Z, lookbehind widths) that this tester approximates using JavaScript's engine. Results should match for the common 95% case.

Common errors

FAQ

Related tools

Pair the Java regex tester with the general regex tester, cheat sheet, and formatter. You can also browse the full Validators category for more options.