Regex Tester
Test regular expressions against text and inspect matches quickly.
Test patterns against text to validate match logic, debug extraction rules, and quickly reason about regular expressions.
What is this tool?
Regular expressions are patterns used to match, validate, and extract data from text. They are common in validation, log processing, and text cleanup tasks. A regex tester helps developers experiment with patterns safely and inspect the exact matches before using them in code or automation.
Example
Pattern
Matches capitalized words
\b[A-Z][a-z]+\b
Text
Sample input
Alice and Bob both shipped updates on Friday.
Why use Cassidor?
- Useful for debugging validation rules and text extraction.
- Helps verify regex behavior before embedding it in code.
- Simple browser-based testing for quick iteration.
Frequently asked questions
What is a regex used for?
It helps match patterns in strings, such as IDs, emails, dates, or text fragments.
Why is my regex not matching?
Common reasons include incorrect escaping, unsupported flags, or a pattern that does not match the actual input shape.
What are flags?
Flags such as g and i modify how the regex is applied, such as global matching or case-insensitive matching.
Should I use regex for parsing HTML or JSON?
Usually not. Dedicated parsers are safer and more maintainable for structured data.
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