Test regular expressions in real time with highlighted matches, group capture details, and match count. Toggle flags (g, i, m, s, u), pick from common patterns, and use replace mode with backreferences.
LevnTools Regex Tester lets you format, validate, and transform your code directly in your browser. Everything runs locally in your browser — your code and data never leave your device. Unlike cloud-only alternatives that require uploads and accounts, this tool is completely free with no usage limits or watermarks. It is designed for developers debugging API responses, DevOps engineers working with configuration files, students learning data formats — anyone who needs a fast, reliable developer tool without the overhead of installing software. Just open the page and start working.
Regex Tester is used by a wide range of people. Explore how different groups use this tool:
Format, beautify, minify, and validate JSON with syntax highlighting.
Encode and decode Base64 with UTF-8 support and file-to-data-URI.
Encode, decode, and parse URLs with editable query parameters.
Convert text to camelCase, snake_case, kebab-case, and 7 more.
Convert between metric and imperial length units.
Type your regex pattern in the pattern field and your test text in the textarea. Matches are highlighted in real time with color-coded spans. Each match shows its full text, index position, and any capture groups.
The tool supports five JavaScript regex flags: g (global — find all matches), i (case insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), and u (Unicode).
Yes. Switch to Replace mode, enter your regex and replacement string. The tool shows the replaced output. You can use $1, $2, etc. for capture group backreferences in the replacement.
Yes. Click any common pattern button (Email, URL, Phone, IP, Date, Hex Color, HTML Tag, CSS Class, Number, Whitespace) to load a pre-built regex. You can then modify it to suit your needs.
Yes. The tool uses JavaScript native RegExp. All evaluation happens in your browser with a 100ms debounce. No data is sent to any server. Invalid patterns show an error message immediately.