Interactive Regex Tester & Debugger - 100% Client-Side
Test JavaScript regular expressions in real-time with visual match highlighting, capture group decomposition, substitution testing, and ReDoS safeguards.
100% Local Execution: Your regular expressions and target text remain private and are evaluated entirely within your browser.
All file encoding, rendering, and transformations run inside local browser memory.
Key Features & Performance Capabilities
Live Match Highlighting Overlay
Matches are highlighted immediately in the target text with character position indices and real-time execution timing.
Structured Group Breakdown Table
Inspect full matches alongside individual numbered capture groups ($1, $2, etc.) in an organized tabular view.
Interactive Substitution / Replace Mode
Test replacement patterns with live output preview and group backreference support ($1, $&, $`).
Built-In Syntax Cheat Sheet & Presets
Instant access to syntax documentation and 1-click presets for emails, URLs, dates, UUIDs, IPv4 addresses, and HTML tags.
How to Use Regex Tester & Debugger
Enter Regular Expression
Type your regex pattern into the pattern bar, or select a preset pattern from the quick-access library.
Configure Flags
Toggle Global (g), Case-Insensitive (i), Multiline (m), DotAll (s), or Unicode (u) flags to adjust engine behavior.
Provide Test Text
Paste your target string into the editor box to observe live highlighted matches and capture group extractions.
Inspect Matches or Test Replacement
View detailed match indices in the Match Details table or switch to Substitution mode to test regex find-and-replace.
Mastering Regular Expressions with Safe Browser-Native Tools
The Power of Regular Expression Engines
Regular expressions (regex) define search patterns for string matching, lexical parsing, and text transformation. Modern ECMAScript regex engines offer powerful features including non-capturing groups, lookaheads, lookbehinds, and unicode property escapes. Our tester lets you build and verify complex patterns interactively.
Protection Against ReDoS (Catastrophic Backtracking)
Regular Expression Denial of Service (ReDoS) occurs when an ambiguous pattern with nested quantifiers forces an engine into exponential combinatorial backtracking. VicanTools incorporates iteration limits and timeout protection to keep your browser smooth and responsive during testing.
Frequently Asked Questions (FAQ)
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