Regex Tester
tools/development.regex-tester.editor.flags_hint
Why Use Our Regex Tester?
Regular expressions (regex) are powerful pattern-matching tools used in nearly every programming language. Debugging regex can be challenging — a single wrong character changes the entire match behavior. Our real-time regex tester highlights matches as you type, shows capture group details, and supports all JavaScript regex flags, making it the fastest way to build and validate your patterns.
Live Match Highlighting
See matches highlighted in real-time as you type — no need to press any button
Capture Group Details
View all capture groups, their indices, and matched values for each match
Full Flag Support
Toggle g, i, m, s, u, y flags independently and see how they affect matches instantly
How to Test Regex in 3 Steps
Enter Your Pattern
Type your regular expression in the pattern field (without surrounding slashes)
Select Flags
Toggle g (global), i (case-insensitive), m (multiline) and other flags as needed
Paste Test String
Enter the text to test against — matches will be highlighted automatically
Common Regex Use Cases
Form Validation
Validate email addresses, phone numbers, URLs, postal codes, and custom formats
Text Search & Replace
Find and replace patterns in code editors, log files, and text processing pipelines
Log File Parsing
Extract structured data (IPs, timestamps, error codes) from unstructured log files
Input Sanitization
Strip or replace dangerous characters in user input before storing or displaying
Regex Best Practices
✓ Use Anchors for Exact Matches
Use ^ and $ to anchor patterns to the start and end of a string, preventing partial matches
✓ Use Non-Capturing Groups When Possible
Use (?:...) instead of (...) when you don't need to capture the group, improving performance
✓ Escape Special Characters
Characters like . * + ? ( ) [ ] { } | ^ $ \ have special meaning — escape with \ when you want literal matches
✓ Test Edge Cases
Always test with empty strings, Unicode characters, very long inputs, and boundary conditions
❓ Frequently Asked Questions
What regex flavor does this tester use?
This tester uses JavaScript's built-in RegExp engine, which follows the ECMAScript standard. It supports all JS regex features including lookaheads, lookbehinds (ES2018+), named capture groups, and Unicode property escapes.
What's the difference between the g and m flags?
The g (global) flag finds all matches in the string instead of just the first one. The m (multiline) flag makes ^ and $ match the start/end of each line rather than the entire string. They serve different purposes and can be combined.
How do I match a literal dot or asterisk?
Escape them with a backslash: \. matches a literal dot, \* matches a literal asterisk. In a character class [ ], most special characters lose their special meaning, except ] \ ^ -.
Why does my regex match too much?
You're likely using greedy quantifiers. The * and + quantifiers are greedy by default and match as much as possible. Add ? to make them lazy: *? or +? will match as little as possible.