ChatGPT Coding beginner

Regex Pattern Builder and Explainer

Added Apr 1, 2026

You are a regex expert. I need a regular expression pattern that [PATTERN_PURPOSE] for use in [PROGRAMMING_LANGUAGE]. Here are examples of strings that should MATCH: [MATCH_EXAMPLES]. Here are examples of strings that should NOT match: [NON_MATCH_EXAMPLES]. Please: 1) Write the regex pattern, 2) Explain each component of the pattern in plain English using a visual breakdown, 3) Provide test cases covering edge cases I might not have considered, 4) Show a code snippet demonstrating how to use this pattern in [PROGRAMMING_LANGUAGE] with proper error handling, 5) Note any performance concerns for large-scale text processing, and 6) Offer a simpler alternative if the pattern is complex, even if it sacrifices some edge case coverage.

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About This Prompt

Regular expressions are notoriously difficult to write, read, and debug, yet they are essential for text processing, validation, and data extraction. This prompt generates correct regex patterns with the educational breakdown you need to actually understand and maintain them. The requirement for both matching and non-matching examples forces you to think through your requirements precisely, while the edge case test suggestions catch scenarios you may not have considered. The simpler alternative option acknowledges that the perfect regex is sometimes worse than a good-enough one that your team can maintain.

Variables to Customize


[PATTERN_PURPOSE]

What the regex should do

Example: validates email addresses including subdomains and plus-addressing


[PROGRAMMING_LANGUAGE]

Language for syntax and code example

Example: JavaScript


[MATCH_EXAMPLES]

Strings that should match

Example: [email protected], [email protected], [email protected]


[NON_MATCH_EXAMPLES]

Strings that should NOT match

Example: user@, @domain.com, [email protected], user@domain, user [email protected]

Tips for Best Results

Always test regex patterns against real-world data, not just your examples
Use named capture groups for extraction patterns to make code more readable
Consider using a library like validator.js for common validations instead of raw regex

Example Output

## Pattern
```
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
```

## Breakdown
- `^` - Start of string (ensures no leading characters)
- `[a-zA-Z0-9._%+-]+` - One or more valid local-part characters (letters, digits, dots, underscores, percent, plus, hyphen)
- `@` - Literal @ symbol (exactly one)
- `[a-zA-Z0-9.-]+` - One or more valid domain characters (supports subdomains via dots)
- `\.` - Literal dot before TLD
- `[a-zA-Z]{2,}` - TLD must be at least 2 letters
- `$` - End of string

## Edge Cases to Test
- `[email protected]` (minimum valid email) - Should MATCH
- `[email protected]` (IP address domain) - Currently does NOT match...

regex pattern-matching validation text-processing