About Regex Tester & Validator
Product Documentation, Architecture & Offline Privacy Verification
What It Does
Test and validate JavaScript regular expressions with live matches, capture groups, and regex flags while keeping your data private in the browser.
How It Works
Key Features
- Live Matching: Test your regular expression instantly against text and immediately see matched results and total counts.
- Capture Group Extraction: Automatically extract both numbered and named capture groups from your matches for easy inspection.
- 100% Client-Side Privacy: Regex patterns and test text never leave your browser. Zero network requests mean zero data leaks.
- ReDoS Protection: Safeguarded against catastrophic backtracking using execution timeouts and strict boundary limits to keep your browser fast.
Limitations & Compatibility
Frequently Asked Questions
What is a regex tester?
A regex tester is a tool that allows you to write, test, and validate regular expressions against a sample text string. It highlights matches and extracts capture groups to help you refine your patterns.
Is this regex tester free?
Yes, this regex tester is completely free to use without any usage limits.
Does KreateKode send my regex to a server?
No. The Regex Tester & Validator processes your regular expressions entirely locally in your browser. KreateKode never transmits your patterns or test strings to any server, ensuring complete privacy for your sensitive data.
What regex syntax does KreateKode support?
KreateKode uses the native JavaScript RegExp engine. It fully supports standard ECMAScript regular expression syntax, including lookaheads, lookbehinds, non-capturing groups, and named capture groups.
What do the g, i, m, s, u, y, and d flags mean?
These are JavaScript RegExp flags. `g` (global) finds all matches rather than stopping at the first. `i` (ignoreCase) makes the match case-insensitive. `m` (multiline) makes ^ and $ match the start/end of lines. `s` (dotAll) allows . to match newlines. `u` (unicode) treats the pattern as a sequence of Unicode code points. `y` (sticky) matches only from the index indicated by lastIndex. `d` (hasIndices) generates indices for substring matches.
Can I test capture groups?
Yes. The tool automatically extracts and displays both numbered capture groups (e.g., $1, $2) and named capture groups for every match found.
Why does my regular expression fail?
Common reasons include unescaped special characters, unclosed parentheses or brackets, invalid quantifiers, or using syntax unsupported by the JavaScript RegExp engine. Check the error banner for specific syntax issues.
What causes catastrophic regex backtracking?
Catastrophic backtracking occurs when a regex engine uses exponential time to evaluate a complex pattern (like nested quantifiers) against a string that almost matches. This tool limits execution time and string size to protect your browser from freezing.
Is a regex the same as a parser?
No. Regular expressions are finite state machines ideal for pattern matching regular languages. They cannot reliably parse nested structures like HTML or fully validate complex grammars.
Can regex validate an entire email address?
While regex can quickly check if a string looks like an email address, it cannot perfectly validate all email formats permitted by the RFC standards. Complex email validation regexes are often fragile and prone to ReDoS vulnerabilities.
Does this tool work with Unicode text?
Yes. The JavaScript RegExp engine supports Unicode. You can use the `u` flag to safely parse emojis, Arabic, CJK, and other non-ASCII characters.
Ready to use Regex Tester & Validator?
100% private, instant offline processing directly in your browser with zero data retention.
