About this tool
Test a JavaScript regular expression, flags and sample text. Reports each match and its character index; unsafe code is never evaluated. The operation runs locally and is useful for inspection, debugging and documentation.
How to use
- 1Enter or paste the source value.
- 2Adjust the relevant pattern, path or base.
- 3Review and copy the structured result.
Benefits
- Immediate developer feedback.
- Copy-ready output.
- No code execution or upload.
Test patterns against representative and hostile inputs
Practical example
A pattern that matches one sample email can still accept trailing text or reject valid international addresses. Include expected matches, expected failures, empty input and unusually long input in the test set.
Interpreting the result
Read both match values and capture groups. Add anchors only when the whole string must match, and document flags because global, multiline and case-insensitive modes change behavior.
Limits and common mistakes
Browser regular expressions follow JavaScript semantics. Complex nested quantifiers can be slow, and regex is not a safe general parser for HTML or arbitrary programming languages.
Frequently asked questions
Does the tool contact a live server?+
No. It analyzes only the values entered in the browser.
Should output be validated in the target project?+
Yes. Runtime and project rules can differ.