Regex Tester Guide
Reference for testing JavaScript regular expressions with sample text, flags, capture groups, escaped characters, and match review.
Quick answer
Use the Regex Tester to run JavaScript regular expressions against sample text and inspect matches.
What this tool does
The tool helps test patterns, flags, match indexes, and capture groups before using a regex in code, cleanup scripts, or content QA.
Supported input
- JavaScript regex pattern
- Common regex flags
- Multiline sample text
- Capture groups
- Copy-ready match output
Data handling and processing behavior
Processing is handled in the browser for this tool based on the current public implementation. Avoid pasting sensitive logs or personal data unless you have reviewed the implementation and your own data handling requirements.
Step-by-step use
- Paste representative sample text
- Enter the regex pattern
- Choose flags deliberately
- Review matches and groups
- Test positive and negative examples before reusing the pattern
Common errors
Testing only clean samples. Include messy cases that should not match.
Forgetting flags. Case-insensitive, global, multiline, and unicode flags change behavior.
Using regex where a parser is better. Complex HTML, JSON, and language grammars often need structured parsing.
Limits
The tool tests JavaScript regular expressions. Other languages or engines may support different syntax and behavior.
Next steps
- Regex Escape Tool — escape literal text before pattern building
- Text Cleaner — normalize sample text before testing
- Diff Checker — compare cleanup output