Regex Tester
Test and debug regular expressions against text strings with live group matching.
Regex Tester & Debugger
About Regex Tester
The Regex Tester & Debugger is a real-time JavaScript regular expression testing utility. It highlights regex pattern matches, captures expression groups, provides instant regex syntax error diagnostics, and supports global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u) flags with 100% browser-native privacy.
How to Use Regex Tester
Step 1
Type or paste your regular expression pattern into the Regex input box.
Step 2
Toggle active regex flags (e.g., Global "g" or Case-Insensitive "i").
Step 3
Paste test string data into the test text area to view real-time match highlights.
Practical Use Cases for Regex Tester
Form Input & Data Validation
Design and test regex patterns for emails, phone numbers, postal codes, and passwords before putting them in production code.
Log File Data Extraction
Extract IP addresses, timestamps, HTTP status codes, or user IDs from server log entries using capture groups.
Text Search and Replace Debugging
Verify complex regex substitution rules and regex backreferences before running batch refactoring scripts.
Input & Output Examples
Testing Email Address Pattern
Regex: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ | Test: user.name@example.comMatch 1: user.name@example.com (Start: 0, End: 21)
Key Features & Performance
- ✓Real-time regex pattern evaluation with match highlight overlays.
- ✓Supports all JavaScript RegExp flags: g, i, m, s, u, y.
- ✓Capture group and named backreference extraction table.
- ✓100% Client-Side execution guarantees private text payloads remain in local memory.
Key Terminology & Definitions
Regular Expression (Regex)
A sequence of characters that forms a search pattern used for text string parsing, validation, and replacement.
Capture Group
A sub-pattern enclosed in parentheses () that isolates matching substrings for retrieval or backreferencing.