Online Regex Tester & Debugger
Compose, test, and debug regular expressions in real-time. Inspect capture groups, replace matched text, explore popular patterns, and export ready-to-run JavaScript, Python, and PHP regex snippets.
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What is a Regular Expression (Regex)?
A Regular Expression (commonly abbreviated as Regex or RegExp) is a standardized sequence of characters that specifies a search pattern in text. Used across programming languages including JavaScript, Python, PHP, Java, and Go, regular expressions allow software developers to validate input formats (such as email addresses, phone numbers, and URLs), parse string tokens, extract capture groups, and perform complex string transformations.
The NexTools Online Regex Tester & Debugger runs in real-time within your web browser using modern ECMAScript regular expression engines. It provides instant visual match highlighting, detailed capture group inspection, string substitution, and automated code snippet generation with zero latency and 100% data privacy.
Key Capabilities & Features
Live Syntax Match Highlighting
Visualizes every match in contrasting colors directly against your test string as you type, updating in single-digit milliseconds.
Capture Group Decomposition
Breaks down numbered capture groups ($1, $2) and full matches with exact zero-based start and end index positions.
Real-Time String Substitution
Test search-and-replace rules with backreferences (e.g., $& for full match, $1 for Group 1) with instant preview output.
Multi-Language Code Export
Generates clean, production-ready syntax snippets for JavaScript (RegExp.test / exec), Python (re.search / findall), and PHP (preg_match_all).
Frequently Asked Questions
What do the regex flags (g, i, m, s, u) mean?
g (Global): Finds all matches rather than stopping at the first match.
i (Ignore Case): Makes matching case-insensitive.
m (Multiline): Treats ^ and $ as beginning and end of each individual line.
s (DotAll): Allows the dot (.) to match newline characters.
u (Unicode): Treats the pattern as a sequence of Unicode code points.
Is this regex tester compatible with Python and PHP?
Yes. The tester is powered by JavaScript's modern RegExp engine, which shares 98% of its syntax with PCRE (PHP) and Python's re module. The Code Snippet generator automatically formats the syntax for your target language.
Are my strings or proprietary logs sent to any server?
No. All regular expression testing, parsing, and replacement occurs entirely client-side in your browser. Your confidential log files and strings never leave your machine.