RegEx Tester & Debugger
Test and debug regular expressions online in real time. Highlight match groups, test flags (g, i, m, s), and validate regex patterns with JavaScript engine accuracy.
support@toolnest.devbilling.team@payments.example.comalex_smith99@engineering.orgWhat is RegEx Tester & Debugger?
RegEx Tester is an interactive developer tool that tests regular expression patterns against test strings, displaying match indexes, capture groups, and flag combinations.
How RegEx Tester & Debugger Works
The tool compiles your pattern and flags using the browser's native JavaScript `RegExp` engine, executing `RegExp.exec()` in a loop to extract matches and capture groups with exact string offsets.
Key Features
- ✓Real-time match highlights with match count badges
- ✓Support for standard JS flags: `g` (global), `i` (ignore case), `m` (multiline), `s` (dotAll)
- ✓Detailed capture group inspection table
- ✓Syntax error detection for invalid regex tokens
Common Use Cases
- •Prototyping data validation patterns (emails, phone numbers, UUIDs, postal codes)
- •Testing capture groups for log parsing and text extraction scripts
- •Debugging regex flags such as global (`g`), case-insensitive (`i`), and multiline (`m`)
Examples & Sample Data
Matching Email Addresses
Pattern: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
Test String: Contact us at support@toolnest.dev for help.Match 1: support@toolnest.dev (Index: 14 to 34)Captures valid RFC 5322 email patterns.
Technical Notes & Limitations
Runs using the browser's native JavaScript ECMAScript RegEx flavor. Advanced features unique to PCRE or Python (such as atomic groups or possessive quantifiers) are not supported by standard JavaScript engines.
100% Client-Side Privacy Guarantee
Patterns and test strings remain 100% client-side.
How to Use RegEx Tester & Debugger
- 1
Enter your regular expression pattern and select active flags.
- 2
Paste your test text into the test area.
- 3
Review highlighted matches and capture groups in real time.