Regex Tester Online: Build, Test, and Debug Regular Expressions

Why a regex tester matters

Regular expressions are powerful but easy to get wrong. A tester shows matches in real time so you can validate logic before shipping code.

Build patterns step by step

Start with a small target string, add groups, then expand with alternation and optional parts. Keep flags like g, i, and m explicit.

• Start small and add one token at a time
• Use capture groups intentionally
• Test with edge cases

Common pitfalls

Greedy quantifiers often match more than expected. Use lazy modifiers and anchors to narrow matches.