Regex Tester

How to Use the Regex Tester

1. Enter your regular expression pattern in the "Pattern" input field.
2. Toggle regex flags (g, i, m, s) by clicking the flag buttons to customize matching behavior.
3. Type or paste your test string in the "Test String" area below.
4. View live-highlighted matches and detailed match information in the Results section.
5. Optionally enter a replacement string to preview find-and-replace operations.
6. Use the "Common Patterns" buttons to quickly load frequently used regex patterns.

Technical Overview & Use Cases

This tool uses JavaScript's native RegExp engine to provide real-time regex testing with syntax validation, match highlighting, group capture display, and replacement preview. It supports all standard flags (global, case-insensitive, multiline, dotAll) and provides instant feedback as you type.

• Development & Debugging: Test and refine regex patterns before implementing them in code — validate email formats, URL parsing, or data extraction rules.
• Data Extraction: Experiment with capture groups to extract specific portions of text, such as dates, phone numbers, or structured identifiers from raw data.
• Find & Replace: Preview replacement operations with group references ($1, $2) before applying them to production data or source code.

Privacy & Security Guarantee

This tool is part of the FAK LAB ecosystem, founded by Faizan Ahmad Khan Khichi. All regex processing happens 100% client-side in your browser using JavaScript's native RegExp engine. Your patterns and test strings are never sent to any server, stored, or logged — everything stays on your device.

Frequently Asked Questions

Which regex flavor does this tool use?

This tool uses JavaScript's native RegExp engine, which supports ECMAScript regex syntax including lookahead, lookbehind (in modern browsers), named groups, and Unicode property escapes.

What do the regex flags mean?

g (global) finds all matches; i (case-insensitive) ignores letter case; m (multiline) makes ^ and $ match line boundaries; s (dotAll) makes the dot match newlines.

Can I use capture groups and backreferences?

Yes! Use parentheses for capture groups and reference them in the replacement string with $1, $2, etc. The results panel shows each captured group's content alongside the full match.