Regex Tester - Regular Expression Tester & Debugger Free

How to Use the Regex Tester

1. Enter your pattern — type your regular expression without delimiters (e.g. \d{3}-\d{4} for matching phone number patterns)
2. Set flags — toggle g (global match all), i (case-insensitive), m (multiline), s (dotall), u (unicode), or y (sticky)
3. Add test string — paste or type the text you want to search through
4. Set replacement — optionally enter a replacement string with backreferences like $1-$2 to transform matches
5. View results — see match count, highlighted matches in the text, and the replaced output if applicable

Features

• Real-time matching — see matches highlighted instantly as you type your pattern or test string
• All regex flags — supports g, i, m, s, u, and y flags for complete pattern control
• Match highlighting — matched text is clearly highlighted in the output area
• String replacement — test regex replacements with numbered and named backreferences
• Error feedback — invalid regex patterns show descriptive error messages to help you debug
• Match count — shows the total number of matches found in your test string

Use Cases

• Form validation — build and test patterns for email addresses, phone numbers, ZIP codes, and credit cards
• Log file parsing — extract specific entries from server logs, error reports, or structured text files
• Data cleaning — find and replace formatting issues in CSV exports or user-submitted data
• Web scraping — develop and refine patterns for extracting information from HTML or JSON
• Code refactoring — test find-and-replace operations before running them across your codebase

FAQ

Why is my regex not matching anything?

Common causes include missing flags (like case-insensitive), incorrect escaping of special characters, or pattern logic errors. Try simplifying your pattern and testing it piece by piece with shorter test strings.

What’s the difference between capturing and non-capturing groups?

Capturing groups (...) store matched text for backreference use like $1. Non-capturing groups (?:...) group parts of your pattern without storing them — use them when you need grouping but don’t need the captured value.

Does this tool support lookahead and lookbehind?

Yes. The tester supports both positive (?=...) and negative (?!...) lookaheads, as well as positive (?<=...) and negative (?<!...) lookbehinds in browsers that support ES2018.

Is my data stored or sent anywhere?

No. Everything runs entirely in your browser. Your test strings and regex patterns never leave your computer.

Tips

• Start with simple patterns and gradually add complexity — test each change
• Use the g flag when you want to find all matches, not just the first one
• Escape special characters (. * + ? [ ] ( ) { } ^ $ | \) with a backslash when you want to match them literally
• When in doubt about a quantifier, * matches zero or more, + matches one or more, ? matches zero or one