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Regex Tester

Test and debug regular expressions with live matching and highlights

Pattern

//g

Test String

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What is Regex Tester?

Free online regex tester to test and debug regular expressions against sample text with real-time match highlighting.

Enter your regex pattern and flags, then see every match highlighted instantly in your test string. The tool shows detailed match information including capture groups, indices, and match count, so you can validate a pattern as you build it. Use it to test regex online for JavaScript, check a Python-style pattern, or debug an expression that is not matching what you expect. It works for any language that supports standard regex syntax. Everything runs in your browser, so your patterns and test data never leave your device. No signup required.

How to Use Regex Tester

1Enter your regular expression pattern in the pattern field
2Select the flags you need: global (g), case-insensitive (i), multiline (m), dotAll (s)
3Type or paste your test string in the text area below
4See matches highlighted in real time with detailed match information

Frequently Asked Questions

This tool uses JavaScript's built-in RegExp engine. JavaScript regex supports most standard features including character classes, quantifiers, lookahead/lookbehind, named capture groups, and Unicode escapes. The syntax is compatible with most other regex flavors.

The 'g' flag enables global matching (find all matches, not just the first). The 'i' flag makes matching case-insensitive. The 'm' flag makes ^ and $ match line boundaries instead of string boundaries. The 's' flag makes the dot (.) match newline characters.

Most regex syntax is shared across languages (JavaScript, Python, Java, PHP, etc.). However, some advanced features like possessive quantifiers or conditionals may differ. This tool is best for testing standard patterns that work across all major languages.

After a pattern matches, the tool lists each match along with its numbered and named capture groups and their positions in the string. This helps you confirm that a group like (\d{4}) is capturing the part of the text you intended.

Common causes are a missing global flag when expecting multiple matches, unescaped special characters such as . or ( taken literally, or anchors like ^ and $ that do not behave as expected without the multiline flag. Toggle the flags and check the highlighted output to narrow down the issue.

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What is Regex Tester?

Free online regex tester to test and debug regular expressions against sample text with real-time match highlighting.

Frequently Asked Questions