Regex Tester
Test regular expression patterns in real-time
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The Regex Tester lets you write regular expression patterns and instantly see matches highlighted in your test text. It supports flags (global, case-insensitive, multiline), displays capture groups, and includes presets for common patterns like email, URL, phone number, and IP address. Perfect for building and debugging text validation, data extraction, and string manipulation patterns used across all programming languages.
๐ How to Use
- Enter a regex pattern
- Enter text to test against
- Matching parts are highlighted
- Check presets for common patterns
โจ Features
- โReal-time match testing
- โMatch result highlighting
- โFlag support (g, i, m)
- โCommon pattern presets
- โCapture group display
๐ก Use Cases
- โขBackend Developer: Test input validation patterns (email format, password rules, etc.) before implementing them in production code.
- โขFrontend Developer: Build and verify form validation regex patterns in real time before adding them to client-side logic.
- โขData Engineer: Craft patterns to extract specific data from log files, CSV exports, or unstructured text.
- โขSystem Administrator: Test regex patterns for grep, sed, and awk commands before running them on live systems.
- โขStudent: Learn regular expression syntax visually by watching matches update in real time as you modify the pattern.
- โขQA Engineer: Create patterns to validate test data formats and ensure data meets expected structures.
๐ฏ Tips
- โธStart with a preset pattern for email or URL, then customize it to match your specific requirements.
- โธToggle the g (global) flag to find all matches in the text. Without it, only the first match is returned.
- โธBreak complex patterns into smaller groups, test each independently, then combine them for easier debugging.
- โธTo match special characters (. * + ?) literally, escape them with a backslash (\).
- โธEnable the m (multiline) flag when testing multi-line text so ^ and $ match the start and end of each line.
โ FAQ
Q. How do I write an email regex?
A. Select the email pattern from presets. A basic email validation pattern is provided.
Q. How do I set flags?
A. Select g (global), i (case insensitive), m (multiline) flags next to the pattern input.
Q. What are capture groups?
A. Parentheses () create capture groups that extract specific parts of a match. For example, you can extract just the year from a date or the domain from a URL. Captured groups are displayed separately in the results.
Q. Do regex patterns differ between programming languages?
A. Core syntax is mostly the same, but supported features vary by language. This tool uses the JavaScript regex engine, so some advanced features like lookbehind may depend on your browser version.
Q. How can I avoid regex performance issues?
A. Patterns with excessive backtracking like (a+)+ can cause performance problems. Write specific patterns, and use lazy quantifiers (*?, +?) instead of greedy ones when matching variable-length content.