About the Regex Tester & Debugger
Regular expressions are one of the most powerful — and most notoriously confusing — tools available to developers. This Regex Tester & Debugger lets you write a pattern, apply flags, and instantly see every match highlighted against your own sample text, along with captured groups, so you can iterate quickly instead of guessing and re-running code.
This tool is useful for developers validating form input patterns (emails, phone numbers, passwords), data engineers writing extraction or cleaning scripts, and students learning regex syntax step by step through live feedback. Everything runs using your browser's native JavaScript regex engine, so behavior matches exactly what you'd get inside real JavaScript code.
To use it, type your pattern into the regex field (without the surrounding slashes) and set flags such as g (global), i (case-insensitive), m (multiline), or s (dot matches newline). Paste your sample text into the test area below. Matches are highlighted in the text as you type, and a panel lists each match along with its index position and any captured groups, making it easy to confirm your pattern behaves as intended before pasting it into your codebase.
For example, testing the pattern \b[\w.-]+@[\w-]+\.[a-zA-Z]{2,}\b with the global flag against a block of text containing several email addresses will highlight every valid-looking email and list them individually — instantly showing whether your pattern is too strict (missing valid emails) or too loose (matching things that aren't emails).
A very common mistake is forgetting the global (g) flag when you expect to find multiple matches — without it, only the first match is returned. Another frequent issue is not escaping special regex characters (like . or ( ) when you actually want to match a literal period or parenthesis, causing unexpected matches. This tool clearly shows exactly what text is being matched, which makes these mistakes obvious immediately rather than only surfacing as a bug much later in production code.
Tip: build complex patterns incrementally — start with a simple pattern that matches the easy cases, verify it live against your sample text, then add complexity piece by piece (optional groups, alternation, lookaheads) while re-checking matches after every change. This is far more reliable than trying to write a complicated regex correctly in one attempt.