Regex Tester
Test and debug regular expressions in real time with syntax error explanations, match highlighting, and capture group breakdowns.
Quick Answer & Understanding Your Result
A Regex Tester allows you to test, debug, and validate JavaScript and PCRE regular expressions in real time, providing instant match highlighting, capture group extraction, and syntax error breakdowns.
Core Regular Expression Testing Features
- Real-Time Match Highlighting: Color-codes full matches and numbered/named capturing groups (
(?<name>...)) instantly. - Global & Multiline Flags (`g`, `i`, `m`, `s`, `u`, `y`): Full support for case-insensitivity, dotAll mode, and Unicode code point matching.
- Detailed Group Table: Displays matched indexes, string lengths, and nested sub-groups.
Development Applications
- Form Input Validation: Testing email, phone number, password, and postal code validation patterns.
- Log & Text Parsing: Extracting structured fields from web server access logs and API responses.
Enter a regular expression and test string above to inspect matches in real time.
Formula & Calculation Logic
Technical Specification & ASTRegex engine evaluation:
- Compiles regular expression AST and evaluates matching states against target string using ECMAScript RegExp semantics.
Step-by-Step Guide
Enter Regex Pattern & Flags
Type pattern (e.g. ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$) and select flags.
Enter Test String
Paste text containing matches or edge case inputs.
Inspect Live Matches & Groups
View highlighted matches and captured group data in 0ms.
Worked Examples Table
| Example | Input Values | Calculated Result | Explanation |
|---|---|---|---|
| Email Address Extraction | Extracted all valid email addresses. | ||
| Email Address Extractor | Provides instant quantitative evaluation for comparative practical analysis. |
Frequently Asked Questions
Evidence-Based Methodology & Authoritative References
ECMAScript Language Specification - RegExp Objects
MDN Web Docs - Regular Expressions Guide
Standard: ISO / W3C / IETF Authoritative Domain Standard
Formula: Match Array = Array.from(testString.matchAll(new RegExp(pattern, flags)))
Last Reviewed: August 21, 2026
Primary Source: ECMAScript Language Specification - RegExp Objects
Reference Document: MDN Web Docs - Regular Expressions Guide
Computation Privacy: 100% client-side 0ms computation, zero data retention
All algorithms, formatters, and data conversions run 100% locally in your browser following official technical standards (RFC, ISO, W3C). Output should be verified prior to mission-critical production deployment.
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Calculated results are modeled based on standard scientific and mathematical formulas. Please verify with domain-specific technical documentation for specialized applications.