Quick Regex Reference
Character Classes
. | Any character except newline |
\d | Digit (0-9) |
\w | Word character (a-z, A-Z, 0-9, _) |
\s | Whitespace |
[abc] | Any of a, b, or c |
[^abc] | Not a, b, or c |
Quantifiers
* | 0 or more |
+ | 1 or more |
? | 0 or 1 |
{3} | Exactly 3 |
{3,} | 3 or more |
{3,5} | Between 3 and 5 |
Anchors
^ | Start of string |
$ | End of string |
\b | Word boundary |
Groups
(abc) | Capture group |
(?:abc) | Non-capturing group |
a|b | a or b |
About Regex Tester
Test and debug regular expressions in real-time. Perfect for developers, data analysts, and anyone working with pattern matching. Supports JavaScript regex syntax with live highlighting and match details.
Real-time pattern testing with live highlighting
Capture group visualization
Quick pattern templates (email, URL, phone, IP, date)
Flags: global, case-insensitive, multiline, dotall
Detailed match index and group information
Common Use Cases:
- Validate email addresses and URLs
- Extract phone numbers from text
- Parse log files and structured data
- Validate form input patterns
- Search and replace operations
- Test regex before using in production code
Frequently Asked Questions
What is a regular expression (regex)?
A regular expression (regex) is a sequence of characters that defines a search pattern. It is used in programming and text processing to match, find, and manipulate strings. Common uses include form validation, data extraction, search and replace, and log parsing.
What regex flags are supported?
This tool supports JavaScript regex flags: g (global — find all matches), i (case insensitive), m (multiline — ^ and $ match line boundaries), and s (dotall — . matches newlines). You can combine multiple flags for complex pattern matching.
What are capture groups in regex?
Capture groups are portions of a regex pattern enclosed in parentheses (). They extract specific parts of a match. For example, in the pattern (\d{3})-(\d{4}), group 1 captures the first 3 digits and group 2 captures the last 4 digits. This tool shows all capture groups for each match.