Regex Tester & Builder
Create and test regular expressions with live pattern matching
Your Regular Expression
Flags
Common Patterns
Build, test, and debug regular expressions with real-time match highlighting directly in your browser. This regex tester supports the full ECMAScript flavor with named capture groups, lookaheads, and Unicode mode — serving as a powerful regex101 alternative that works entirely client-side.
Real-Time Regex Pattern Builder and Debugger
Regular expressions are a foundational tool for string manipulation, input validation, log parsing, and data extraction — but writing and debugging them without immediate feedback is error-prone and slow. A real-time regex tester that highlights all matches, capture groups, and flags as you type dramatically accelerates regex development.
This tool evaluates ECMAScript (JavaScript) regular expressions, the flavor used natively in all modern web browsers, Node.js, and Deno. ECMAScript regex supports named capture groups (`(?<name>...)`), non-capturing groups, lookahead and lookbehind assertions, the `s` (dotAll) flag, the `u` (Unicode) flag, and the `v` (Unicode Sets) flag in modern engines.
All regex evaluation runs in your browser's native JavaScript engine — no data is transmitted to any server. Match results, capture group values, and replacement previews update instantly as you modify either the pattern or the test string, providing the tight feedback loop needed for complex regex development.
Named Capture Groups and Advanced ECMAScript Features
Named capture groups (`(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})`) make complex patterns self-documenting and allow accessing match results by name rather than index. This tool highlights each named group in a distinct color, making it easy to verify that each group captures the intended text. Lookahead (`(?=...)`) and lookbehind (`(?<=...)`) assertions — including negative variants — are fully supported and visualized in the match breakdown panel.
Validating User Input Formats
Build and test patterns for email addresses, phone numbers, URLs, credit card numbers, zip codes, and other user input formats before adding them to form validation logic.
Parsing Log Files and Structured Text
Develop capture group patterns for extracting timestamps, IP addresses, error codes, and structured fields from server logs, access logs, or CSV-like text files.
String Search and Replace Operations
Test find-and-replace patterns with capture group backreferences (`$1`, `$<name>`) before deploying them in code editors, data pipelines, or migration scripts.
- 1
Enter Your Regex Pattern
Type or paste your regular expression into the pattern field (without surrounding slashes). Select flags — `g` (global), `i` (case-insensitive), `m` (multiline), `s` (dotAll), or `u` (Unicode) — using the flag checkboxes.
- 2
Add Your Test String
Paste the text you want to test against in the input panel. All matches are highlighted in real time with different colors for each capture group. Match count and positions are displayed in the results panel.
- 3
Inspect Matches and Capture Groups
The match breakdown panel lists every match with its start/end index and the value of each capture group — both numbered and named. Use the replace panel to preview substitution output with backreference templates.
Real-Time Match Highlighting
All matches and capture groups are highlighted in the test string as you type, with distinct colors per group for immediate visual feedback on pattern correctness.
Named Capture Group Support
Full support for ECMAScript named capture groups (`(?<name>...)`) with color-coded group visualization and named references in the replacement template.
Flag Controls and Unicode Mode
Toggle `g`, `i`, `m`, `s`, and `u` flags with checkboxes. Unicode mode enables proper matching of Unicode categories, emoji, and surrogate pairs.
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