Regex Tester

The Regex Tester lets you write a regular expression, test it against sample text in real time, and instantly see every match highlighted, along with capture groups, match positions, and flag behavior — all without leaving your browser or writing a single line of throwaway test code. Type a pattern, paste your test string, toggle flags like global, case-insensitive, or multiline, and watch matches update live as you refine the expression. Regular expressions are one of the most powerful and most consistently misunderstood tools in programming, used for validating form input like email addresses and phone numbers, parsing log files, extracting structured data from unstructured text, performing bulk find-and-replace operations across a codebase, and writing routing rules in web frameworks. The trouble is that regex syntax is dense and unforgiving — a single misplaced character, an unescaped special symbol, or a misunderstood quantifier can silently turn a pattern that "mostly works" into one that fails on real-world edge cases. Testing interactively against a range of realistic sample inputs, rather than guessing and running a full application to see if it works, is the single best way to write correct, maintainable regular expressions. The tool highlights not just whether your pattern matches, but exactly which characters were consumed by the match and by each capture group, which is invaluable when you're extracting a specific piece of data (like the domain from a URL, or the numeric part of an ID) rather than just checking for a yes/no match. Understanding greedy versus lazy quantifiers is a common sticking point — a greedy ".*" will consume as much text as possible before backtracking to satisfy the rest of the pattern, which often grabs far more than intended when there are multiple similar delimiters in the string, while a lazy ".*?" stops at the first possible match. Testing both variants side by side against tricky sample text is one of the fastest ways to build the right intuition. Common practical patterns that benefit from live testing include email validation, extracting hashtags or mentions from social text, matching URLs, splitting on multiple delimiters, validating password complexity rules, and stripping HTML tags from a string. Because regex flavors differ slightly between JavaScript, Python, PCRE, and others, it's worth confirming which engine you're targeting — this tool uses JavaScript's native regex engine, which is the same one used by browsers and Node.js, so patterns you validate here will behave identically in most modern web and Node backend code. Pair this tool with the URL Encoder when your pattern needs to handle encoded characters, and the HTML Entity Encoder if you're building a pattern to sanitize or strip markup. As with everything on this site, all matching runs locally in your browser using the JavaScript engine already built into it — no pattern or sample text you write is ever sent to a server, which matters when testing regexes against real user data, log excerpts, or proprietary formats.