Regex Tester
Test regular expression patterns in real-time with visual matching results
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Common Patterns
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💡 Pro Tips
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Use Flags: Combine g(global), i(case-insensitive), m(multiline) flags for various matching approaches
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Group Capture: Use parentheses() to capture matched parts as groups and reuse with '$1', '$2'
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Lookahead/Lookbehind: Use (?=pattern) and (?!pattern) to check before/after specific patterns
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Performance: Use lazy quantifiers(*?, +?) instead of greedy ones(*, +) to prevent unnecessary matching
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Replacement Variables: Use '$&' (full match), '$`' (before match), '$''' (after match), '$n' (groups) for dynamic replacement
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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.