Regex Tester — Test Regular Expressions Online

What is a Regex Tester?

A regex tester provides an interactive environment where you enter a regular expression pattern and a test string, and it highlights all matches in real time. It shows captured groups, match positions, and whether the pattern compiles without errors.

Why Use a Regex Tester?

Regex syntax is dense and error-prone. A small typo creates a pattern that matches nothing — or worse, matches everything. Real-time visual feedback shows exactly what your pattern captures, catches syntax errors immediately, and lets you iterate without rerunning code.

Key Benefits

• Live match highlighting as you type
• Shows all captures and groups
• Supports flags: g, i, m, s
• Syntax error messages shown immediately
• No page reload — instant feedback

How to Use Regex Tester

1. Enter your regex pattern (without slashes)
2. Set flags (global, case-insensitive, multiline, etc.)
3. Paste test text
4. Matches highlight in real time
5. Adjust pattern until you get the expected matches

Example Use Case

Writing a validation regex for email addresses. Enter the pattern, paste a list of test emails (valid and invalid), and the highlighter shows which ones match. Adjust the pattern until valid emails highlight and invalid ones don't.

Tips

• Use ^ and $ anchors to match full string, not just a substring
• The g flag finds all matches, not just the first
• Use (?:...) for non-capturing groups
• Escape special characters like . * + ? with backslash