About Regex Tester
This tool helps you debug regular expressions online with live matching, highlighted output, capture-group details, replacement preview, and sed command generation.
Key Features
- Live Matching: Evaluate pattern and input text instantly.
- Flag Controls: Supports
g(global),i(ignore case), andm(multiline). - Highlight Preview: Highlights matched segments in source text.
- Match Details: Shows match items, index positions, and groups.
- Replace Preview: Test replacement text before using it in code.
sedCommand Output: Generate shell-friendly replacement commands.- Quick Templates: Apply common regex templates with one click.
Flag Reference
| Flag | Meaning | Effect |
|---|---|---|
g |
global | returns all matches; replaces all matches |
i |
ignore case | case-insensitive matching |
m |
multiline | ^ and $ work per line |
Steps
- Enter test content in the text area.
- Input the regex pattern (without wrapping
/). - Enable flags (
g,i,m) as needed. - Review match count, highlights, and detail list.
- Add replacement text to preview result and copy output or
sedcommand.
Use Cases
- Form validation rule debugging.
- Pattern verification before batch extraction/cleanup.
- Log parsing and text automation script preparation.
- Terminal replacement command rehearsal.
FAQ
Why are there no matches?
Most cases are caused by incorrect escaping, missing flags, or mismatched anchors.
Why is replacement output unexpected?
Check capture-group references ($1, $2, etc.) and ensure your pattern actually captures those groups.
Is my text uploaded?
No. Processing runs locally in your browser by default.