RegEx Tester & Debugger
Test regular expressions against target text strings instantly.
How to Use RegEx Tester & Debugger
- Paste or type your input string, code snippet, or text block into the regex tester & debugger editor.
- Configure formatting rules, target case, indent spacing, or encoding parameters.
- Click Process to execute the transformation instantly inside browser memory.
- Copy the formatted output or download it as a text file.
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Frequently Asked Questions
What regular expression flags are supported in this tester?
The tester supports all ECMAScript regular expression flags: 'g' (global search for all matches), 'i' (case-insensitive matching), 'm' (multiline mode where ^ and $ match line boundaries), 's' (dotAll mode allowing . to match newlines), 'u' (full Unicode code point support), and 'y' (sticky matching).
Can I paste regex literals formatted with slashes (/pattern/flags)?
Yes. You can enter standard patterns directly (e.g., ^[a-z0-9]+$) or paste full regex literals with enclosing slashes and flags (e.g., /^[a-z0-9]+$/gi). The tester parses the pattern and flags cleanly.
How are capturing groups displayed in the test results?
When your regex contains parenthesized capturing groups (e.g., (\w+)@(\w+\.\w+)), the tester lists the full match string alongside each numbered sub-group (Group $1, Group $2) and the exact character index location.
What is catastrophic backtracking and how can I avoid it?
Catastrophic backtracking (Regular Expression Denial of Service or ReDoS) occurs when nested quantifiers (like (a+)+$) cause the regex engine to explore exponential execution paths on non-matching strings. Avoid nesting quantifiers and use atomic grouping or non-overlapping character classes.
Are regex patterns tested client-side or sent to a server?
All regular expression evaluations execute client-side using your browser's native JavaScript RegExp engine. Your test datasets and proprietary regex patterns remain completely private.