Regular Expression Tester

Free Regular Expression Tester that works offline

Test a JavaScript regular expression against private sample text and inspect every captured value. The JSON report includes match indexes, numbered groups and named groups where supported.

What this regular expression tester does

Regex behavior depends on the language engine and flags. Using the browser directly makes results relevant to client-side JavaScript. Match output is limited to 1,000 entries to protect the interface from runaway zero-width or highly repetitive patterns.

How to use the Regular Expression Tester

1. Enter or paste a JavaScript regular-expression pattern, flags and test text into the tool.
2. Adjust the available options so they match the format and result you need.
3. Choose Test expression and review a JSON report of matches, indexes and capture groups before using it.
4. Copy or download the result, then clear the page if the input was sensitive.

Common uses

• Debugging validation patterns
• Testing extraction expressions against sample logs
• Inspecting named and numbered capture groups
• Learning how JavaScript regex flags change behavior

Private processing and offline access

This tool does not submit your input to a conversion server. Processing takes place inside the browser using local JavaScript and standard Web APIs. After the PWA has been installed or cached, the page and its core features remain available without an internet connection. Closing or clearing the page removes unsaved input; the tool does not create an account or cloud history.

Tips for accurate results

• Avoid catastrophic backtracking on very long input.
• Remember that regex is not a full HTML or programming-language parser.
• Escape backslashes correctly when moving a pattern into a JavaScript string literal.

Frequently asked questions