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Test regular expressions against sample text.
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Does this regex tester send my text anywhere?
No. Regex matching happens entirely in your browser using JavaScript's built-in RegExp engine.
Why do I see a syntax error?
If your pattern contains invalid regex syntax, the RegExp constructor throws an error, which is displayed immediately.
What do the flags (g, i, m, s, u, y) mean?
They control regex behavior: global, case-insensitive, multiline, dot-all, unicode mode, and sticky matching.
How are matches displayed?
Matches are highlighted in the text area and also listed individually with their start/end indexes.
Why does the tester behave differently from Python/PCRE?
This tool uses JavaScript RegExp syntax, which differs from PCRE (used by many other engines). Some constructs may not behave identically.
Can I test multi-line strings?
Yes. The input text area supports multi-line content, and your regex can use the 'm' and 's' flags to modify matching behavior.