Regex Tester
Test and debug regular expressions with real-time highlighting, capture groups, and replace functionality.
Common Patterns
Character Classes
- •
\d- Digit (0-9) - •
\w- Word char (a-z, A-Z, 0-9, _) - •
\s- Whitespace - •
.- Any character - •
[abc]- Any of a, b, or c - •
[^abc]- Not a, b, or c
Quantifiers
- •
*- 0 or more - •
+- 1 or more - •
?- 0 or 1 - •
{n}- Exactly n times - •
{n,}- n or more times - •
{n,m}- Between n and m
Anchors & Groups
- •
^- Start of string - •
$- End of string - •
(abc)- Capture group - •
(?:abc)- Non-capturing - •
(?<name>abc)- Named group - •
a|b- a or b
Tips
- • Use the g flag to find all matches instead of just the first one
- • Escape special characters with backslash:
\.\*\? - • Test your regex with multiple test cases to ensure it works correctly
- • Use capture groups with replace:
$1,$2, etc. - • Named groups can be referenced in replace with
$<name>
Frequently Asked Questions
What are regex flags and when should I use them?
Regex flags modify how pattern matching works. The global flag (g) finds all matches instead of stopping at the first one. The case-insensitive flag (i) ignores letter case. The multiline flag (m) treats each line as a separate string for ^ and $ anchors. These flags are essential for flexible text processing and validation.
How do I test and debug my regular expressions effectively?
Start with simple patterns and gradually add complexity. Test against multiple input samples, including edge cases and invalid data. Use capture groups to extract specific parts of matches. The regex tester shows real-time matches with highlighting, making it easy to verify your pattern works correctly before using it in production code.
What is the difference between capturing groups and non-capturing groups?
Capturing groups, denoted by parentheses (), save matched text for later use and can be referenced with $1, $2, etc. in replacements. Non-capturing groups (?:...) group patterns without saving the match, which is more efficient when you don't need to reference the captured text. Named groups (?<name>...) provide descriptive labels for captured values.
How can I use the regex replace feature for text transformation?
Enter your pattern in the regex field, enable the Replace toggle, and type your replacement text. Use $1, $2, etc. to reference captured groups in your replacement. For example, the pattern (\w+)\s+(\w+) with replacement $2 $1 will swap two words. This is powerful for reformatting data, cleaning text, and batch transformations.
What are common regex patterns for email and URL validation?
For basic email validation, use: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}. For URLs, try: https?://[^\s]+. For phone numbers: \d{3}-\d{3}-\d{4} or \(\d{3}\)\s?\d{3}-\d{4}. Remember that these are simplified patterns; production applications should use more robust validation libraries.
Why is my regex pattern not matching as expected?
Common issues include: forgetting to escape special characters like . * ? + [ ] ( ) | \ ^, not using the global flag (g) to find all matches, incorrect flag combinations, or overly complex patterns. Start simple, test incrementally, and check if you need flags like case-insensitive (i) or multiline (m) mode.