What regex syntax does this support?

JavaScript (ECMAScript) regular expression syntax, which is compatible with most modern programming languages.

What do the flags do?

g = global (find all matches), i = case-insensitive, m = multiline (^ and $ match line boundaries), s = dotAll (. matches newlines).

How do I capture groups?

Wrap parts of your pattern in parentheses, e.g. (\d+). Captured groups are shown in the match list below the test string.

Why test regex in a sandbox before deploying?

Regex bugs are silent — they over-match (false positives) or under-match (missed data) without throwing errors. A live tester reveals edge cases (empty strings, multiline input, special characters) before the regex hits production.

When should I avoid regex entirely?

Don't parse HTML, JSON, or balanced expressions with regex — use a real parser. Regex is best for line-level pattern matching: validation (email, ZIP), extraction (capture groups), and find-and-replace.

Regex Tester

Developer Tools· 30 tools

Free online regular expression tester. Enter a regex pattern and test string to see matches highlighted in real time. Supports flags (g, i, m, s), displays match groups, and shows the total match count. Works with JavaScript regex syntax.

Pattern

//g

Test String

Enter a pattern and test string to see matches highlighted here

Frequently Asked Questions

References

Regular expressions — JavaScript reference — MDN Web Docs

Related Tools

JSON Formatter
Format, validate, and minify JSON in your browser. Pretty-print raw JSON with indentation, catch inline syntax errors, or collapse to one line.
URL Encoder / Decoder
Encode or decode URL components and query strings instantly. Converts special characters to percent-encoded format — essential for debugging web requests.
Hash Generator
Generate SHA-1, SHA-256, and SHA-512 hashes from any text. Results update live as you type — runs via Web Crypto API, data stays in your browser.

Frequently Asked Questions

References and sources

Related Tools