How to use the regex tester
1. Write your regular expression
Enter a pattern in the regex field. Toggle global, case-insensitive, multiline, and dotAll flags to match how your language runtime will evaluate the expression.
2. Paste sample text
Add representative input in the test string area. Matches highlight in real time so you can see which substrings satisfy the pattern.
3. Inspect capture groups
When your pattern includes groups, the tool lists each capture with its matched value. Use this to debug nested or optional groups quickly.
4. Iterate until the pattern is correct
Adjust quantifiers, anchors, and character classes while watching highlights update. Copy the final pattern into your codebase or validation rules.
Common use cases
Form validation rules
Prototype email, phone, or invoice number patterns before adding them to frontend or backend validators.
Log parsing
Test regular expressions against sample log lines to extract timestamps, trace IDs, or error codes reliably.
Code search and refactoring
Validate complex patterns used in IDE or ripgrep searches so they match intended files without false positives.
Data cleaning pipelines
Confirm replacement rules target the right CSV or JSON fields before running them on production datasets.
Interview preparation
Practice explaining how flags and greedy quantifiers change match results with immediate visual feedback.
Frequently asked questions
- Which regex flavor is used?
- The tester uses JavaScript regular expressions, which match browser and Node.js RegExp behavior closely.
- Why does my pattern match unexpectedly?
- Check greedy versus lazy quantifiers, missing anchors (^ and $), and whether the global flag continues matching after the first hit.
- Can I test replacement strings?
- This tool focuses on matching and capture inspection. Use your editor or language REPL for replacement testing.
- Is my test data uploaded?
- No. Matching runs entirely in your browser.