Regex Tester

The Developer's Superpower

Regular Expressions (Regex) are often seen as a dark art. A string of cryptic characters like ^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$ can look intimidating. But once you understand them, they become arguably the most powerful tool in your text-processing arsenal.

Whether you are validating user forms, scraping data from websites, or doing complex find-and-replace operations in your code editor, Regex saves you hours of manual work. It allows you to define a "pattern" of text, and then instantly find every piece of text that matches that pattern.

Our Regex Tester is built to be your sandbox. It gives you immediate, visual feedback. You don't have to guess if your pattern works—you can see the matches highlight in real-time as you type.

How to Use This Tool

This tool is designed for speed and clarity. Here is your workflow:

1. Enter Your Pattern: Type your regex in the top input. e.g., \d{3} to find 3 digits.
2. Set Your Flags: The little box next to the pattern controls the "mode".
   • g (Global): Find all matches, not just the first one.
   • m (Multi-line): Allows ^ and $ to match the start/end of each line, not just the whole string.
   • i (Case Insensitive): Makes a match both "a" and "A".
3. Test Your String: Paste your text content in the large text area.
4. Analyze Results: Look at the "Match Preview" to see the highlighting. Check "Detailed Matches" to see Capture Groups (parts of the match you want to extract).

Core Concepts Crash Course

You can build 90% of regex patterns knowing just these four concepts:

1. Character Classes

These tell the engine "Match a specific type of character".

• \d: Any digit (0-9).
• \w: Any word character (letters, numbers, underscores).
• \s: Any whitespace (space, tab, newline).
• .: Any character at all (except newlines).

2. Quantifiers

These ask "How many times?"

• +: One or more times. \d+ matches "1" and "12345".
• *: Zero or more times.
• ?: Zero or one time (Optional).
• {3}: Exactly 3 times.

3. Anchors

These match a position, not a character.

• ^: Start of the string.
• $: End of the string.

4. Groups

Wrapping part of your regex in parentheses (...) creates a "Capture Group". This is useful if you want to match a full date like "2023-12-25" but extract just the year "2023".

Common Useful Patterns

Here are some "recipes" you can copy and paste:

• Email Address:
  [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
  Matches standard emails like user@example.com
• Standard Date (YYYY-MM-DD):
  \d{4}-\d{2}-\d{2}
• Hex Color Code:
  #?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})
• Strong Password:
  ^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$
  Minimum 8 characters, at least one letter and one number.

Performance Hazard: Catastrophic Backtracking

Be careful with nested quantifiers like (a+)+. If you run this against a long string of "aaaaa" that almost matches but fails at the end, the engine tries every single combination of grouping. This can freeze your browser or crash your server. Always try to be specific!