Regex Tester & Matcher | Debug Regular Expressions

Instantly test, debug, and execute regular expressions locally in your browser. Features real-time syntax highlighting and match extraction.

Regex Tester

Instantly test, debug, and execute regular expressions locally in your browser.

Test String

Match Result0 matches

Hello 123 world! This is a test 456.

Real-Time Pattern Debugging

Test and iterate on complex patterns with instant visual feedback. Our regex debugger highlights capture groups and matches in real-time.

"Securely test patterns against sensitive data without ever sending them to a remote server."

Capture Groups

Visualize individual matches and nested groups instantly.

Pattern Flags

Support for global, case-insensitive, and multiline flags.

Test JavaScript regular expressions with realistic input

Build a pattern, select flags, and inspect full matches and capture groups against sample text. Start with representative positive and negative cases rather than one string that already matches.

Example input

Pattern: ^(?<name>[a-z][a-z0-9_-]{2,15})$
Text: api_user-7

Expected output

Match: api_user-7
Group name: api_user-7

Behavior

Uses JavaScript regular-expression syntax and flags.
Global matching finds more than one non-overlapping result.
Capture groups expose the exact subexpressions that matched.

Limits and edge cases

JavaScript syntax differs from PCRE, RE2, .NET, and other engines.
Nested ambiguous quantifiers can cause catastrophic backtracking.
Regex is rarely the right parser for nested programming languages or HTML.

Processing note: tool input stays in the browser. Readme.now analytics records page usage, not the payload you paste or the generated output.

Authoritative reference: MDN regular expressions guide