How to Use the Regex Tester
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1
Enter your regular expression pattern (e.g., `\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b`).
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2
Toggle active regex flags: `g` (global), `i` (case-insensitive), `m` (multiline), `s` (dotAll).
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3
Paste test sample strings into the test area.
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4
Review real-time match highlights, match indexes, and capture group breakdowns.
Practical Example & Use Case
Common Real-World Scenario
Validating complex email addresses, phone numbers, or extracting key-value pairs from log messages.
Technical Notes & Limitations
Browser Engine Architecture
Complex backtracking patterns are executed in a dedicated Web Worker with a strict execution timeout to guard against browser freezes.
Frequently Asked Questions
What happens if I write a slow or catastrophic regex?
WebUtilities runs the regex in a sandboxed Web Worker; if execution exceeds 1 second, it is safely terminated with a ReDoS warning.