Mastering Regular Expressions
Regular expressions (Regex) are sequences of characters that define a search pattern. This tool helps you test and debug these patterns in real-time.
1. Quick Start
Input: Type your regex in the top box (without the surrounding slashes /).
Test String: Paste the text you want to search through in the larger box below.
The tool will instantly highlight any text that matches your pattern.
2. Understanding Flags
Flags modify how the search is performed:
- g (Global): Find all matches, not just the first one.
- i (Case Insensitive): Matches both 'A' and 'a'.
- m (Multiline): The
^and$anchors match the start/end of each line, not just the whole string. - s (Dotall): The
.character matches newlines as well.
3. Common Syntax
| Character | Description |
|---|---|
. |
Any single character |
\d |
Any digit (0-9) |
\w |
Any word character (a-z, A-Z, 0-9, _) |
[abc] |
Any character in the set |
(...) |
Capture group |
4. Substitution
Use the "Substitution" box to test replacement. You can use $1, $2 to reference
captured groups.
Example: Regex (\d+)-(\d+) with replacement $2/$1 swaps two numbers.
4. Why Choose ToolArc Regex Tester?
🔒 Secure Testing
Regex testing happens in your browser. No need to worry about sending sensitive logs or passwords to a backend server.
âš¡ Real-time Feedback
Type to match. Millisecond response times give you instant feedback, dramatically speeding up complex pattern debugging.
📚 Quick Reference
Built-in cheatsheet for common syntax. Forgot if it's \d or \w? The
sidebar is always there.
5. Regular Expressions in the AI Era
Validating AI-Generated Regex
ChatGPT or Copilot are great at writing regex, but often provide code that "looks right" but fails on edge cases. Never blindly copy AI regex!
Best Practice:
Ask AI for regex → Paste into ToolArc → Paste test text with edge cases
→ Verify before using.
Assist Prompt Engineering
In LLM application development, you often need regex to extract specific fields (like JSON blocks) from raw output. Use ToolArc to quickly build and verify these extraction rules.