Regex Tester

Test regular expression patterns in real-time with visual matching results

Regular Expression Pattern

Common Patterns

Test String

Use Replace Feature

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💡 Pro Tips

Use Flags: Combine g(global), i(case-insensitive), m(multiline) flags for various matching approaches

Group Capture: Use parentheses() to capture matched parts as groups and reuse with '$1', '$2'

Lookahead/Lookbehind: Use (?=pattern) and (?!pattern) to check before/after specific patterns

Performance: Use lazy quantifiers(*?, +?) instead of greedy ones(*, +) to prevent unnecessary matching

Replacement Variables: Use '$&' (full match), '$`' (before match), '$''' (after match), '$n' (groups) for dynamic replacement

Pattern Testing: Build complex regex step by step and test each stage to minimize errors

💼 Practical Use Cases

📋 Data Validation

Validate email, phone, and password formats in registration forms to prevent invalid data input.

🔍 Data Extraction

Automatically extract specific pattern data (URLs, dates, emails) from log files or crawled text.

✏️ Batch Replacement

Find and replace specific patterns in bulk text to save time and reduce manual work.

⚙️ String Parsing

Parse API responses, CSV files, config files to extract and process only necessary information.

Frequently Asked Questions

Regex is too difficult. Where should I start?

Start with the provided presets in 'Common Patterns'. Understand how patterns work by seeing real examples, then gradually modify and learn incrementally.

Should I turn on or off the g flag?

The g(Global) flag is used when you want to find all matches. Without it, it stops after finding the first match. In most cases, enabling the g flag is useful.

What are $1, $2 in the replace feature?

'$1', '$2' etc. reference groups captured by parentheses() in the regex. Example: In (\d{4})-(\d{2}), '$1' is year, '$2' is month.

How do I use the regex I created here in code?

JavaScript: /pattern/flags or new RegExp('pattern', 'flags'). Python: re.compile(r'pattern', flags). Syntax may vary slightly by language, so check documentation.

Can I save complex patterns?

Currently there's no save feature, but you can bookmark in your browser or copy to a separate note. Common patterns are provided as presets.

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