This tester runs your regular expression against sample text and highlights every match as you type, listing capture groups so you can see exactly what each set of parentheses captured. Flags are switchable: g for all matches rather than the first, i for case insensitivity, m so ^ and $ match line boundaries, and s so a dot also matches newlines. Building a pattern incrementally against real sample data is far faster than guessing, and it exposes the two classic traps — a greedy .* swallowing far more than intended, and catastrophic backtracking from nested quantifiers that can hang a server. Patterns follow JavaScript regex syntax, which is close to but not identical to PCRE.
Free, fast, and runs entirely in your browser — no signup, no upload to a server.