Regex TesterDev

Free Regex Tester - Test and debug regular expressions online in real-time with multiple matching modes and flags. Developer essential. Try it now!

/
0 matches

Usage Guide

1. Input Regular Expression

Enter your matching pattern in the regular expression input box. The input box uses /pattern/ format with automatic slash delimiters.

•
Basic Syntax: Use metacharacters like . * + ? to build matching patterns
•
Character Classes: Use \d \w \s to match digits, letters, whitespace
•
Boundary Matching: Use ^ $ to match string start and end
•
Grouping: Use () for capturing groups, (?:) for non-capturing groups
Click the “Regex Presets” button to quickly select common preset patterns including email, phone, URL, ID numbers, etc.

2. Select Match Flags

Choose one or more regular expression flags as needed to control matching behavior:

•
g (global): Global match, find all matches instead of stopping after first match
•
m (multi line): Multi-line mode, ^ and $ match start/end of each line
•
i (insensitive): Case-insensitive matching
•
s (single line): Dot . matches all characters including newlines
•
u (unicode): Enable Unicode mode for proper Unicode character handling
•
d (indices): Generate index information for matches
We recommend enabling g and m flags by default for more comprehensive matching results.

3. Input Test Text

Enter the text content to match in the test text box. Supports multi-line text for testing complex matching scenarios.

•
Real-time Matching: Match results display immediately after text input
•
Multi-line Support: Can input multi-line text to test cross-line matching
•
Highlight Display: Matched text is highlighted in blue

4. View Match Results

The result area on the right displays matching status in real-time, including match count and highlighted matched text.

•
Match Count: Top displays the number of matches found
•
Highlight Display: All matched text is highlighted with blue background
•
Error Messages: If regex syntax is incorrect, error messages are displayed
Use the copy button to quickly copy the regular expression, supporting both plain format and escaped string code format (suitable for pasting directly into code).

FAQ

Q: What is a regular expression?

A: A regular expression (Regex) is a powerful text pattern matching tool used to find, match, and replace text with specific patterns in strings. It is widely used in data validation, text search, content extraction, and is an essential skill for developers.

Q: How to match email addresses?

A: Use the pattern ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ to match standard email addresses. This pattern ensures the email contains an @ symbol, and the domain part includes at least one dot and a top-level domain of 2 or more characters.

Q: What is the difference between greedy and non-greedy matching?

A: Greedy matching (default) matches as many characters as possible, e.g., .* matches the longest possible string. Non-greedy matching adds ? after quantifiers to become .*?, matching as few characters as possible. For example, for text <div>test</div>, greedy pattern <.*> matches the entire string, while non-greedy pattern <.*?> only matches <div> and </div>.

Q: How to match Chinese characters?

A: Use the Unicode range [\u4e00-\u9fa5] to match common Chinese characters. The complete pattern ^[\u4e00-\u9fa5]+$ can validate if a string consists entirely of Chinese characters. We recommend enabling the u flag for proper Unicode character handling.

Q: How to optimize regular expression performance?

A: Optimization tips: ① Avoid excessive use of greedy quantifiers and backtracking ② Use non-capturing groups (?:) instead of capturing groups () ③ Place fixed strings at the pattern start ④ Use character classes [abc] instead of multiple alternatives (a|b|c) ⑤ Avoid nested quantifiers like (a+)+ ⑥ Use anchors ^ $ to limit matching scope.

Q: Is my data safe?

A: Completely safe. All calculations are performed locally in your browser, data is never uploaded to servers, completely offline processing.

Use Cases

Data Validation

Validate user input data format before form submission, such as email, phone number, ID number, etc.

Recommended Configuration:
  • Use ^ and $ to ensure complete matching, avoiding partial matches
  • Enable i flag for case-insensitive validation
  • Use preset common regex patterns to get started quickly
  • Test various edge cases to ensure validation accuracy
Text Search & Extraction

Search and extract content with specific patterns from large text blocks, such as extracting all URLs, email addresses, or phone numbers.

Recommended Configuration:
  • Enable g flag for global search
  • Use capturing groups () to extract needed parts
  • Enable m flag for multi-line text processing
  • Use non-greedy matching *? to avoid over-matching
Log Analysis

Parse and analyze log files, extracting timestamps, IP addresses, error codes, and other key information.

Recommended Configuration:
  • Use \d{4}-\d{2}-\d{2} to match date formats
  • Use IPv4 regex to match IP addresses
  • Enable m flag for line-by-line log processing
  • Use named capturing groups for better readability
Code Refactoring

Use regular expressions in code editors for batch find and replace, quickly refactoring code.

Recommended Configuration:
  • Use \b word boundaries to avoid false matches
  • Use capturing groups and backreferences for replacement
  • Validate in testing tool first before applying to code
  • Save common refactoring patterns for reuse
Data Cleaning

Clean and standardize data, such as removing extra spaces, unifying date formats, extracting structured information.

Recommended Configuration:
  • Use \s+ to match multiple whitespace characters
  • Use trim() with regex to remove leading/trailing spaces
  • Use replacement function to standardize data formats
  • Process complex cleaning tasks step by step

Learning Resources

  • MDN Regular Expressions Guide - Comprehensive syntax reference and examples
  • Regex101 - Online regex testing and debugging tool
  • RegexOne - Interactive regex tutorial
  • Regular Expressions 30-Minute Tutorial - Quick start guide

Discussion & Feedback

0 comments
Me