Regex Tester & Validator

A Regex Tester (Regular Expression Tester) lets you write, test, and debug regular expressions against sample text with live match highlighting, capture group extraction, and detailed match information. Regular expressions are one of the most powerful — and most cryptic — tools in programming. A regex tester eliminates the trial-and-error edit-run-check cycle by giving you instant visual feedback as you type.

What are regular expressions?

A regular expression is a pattern string that describes a set of strings. The pattern /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$/ matches email addresses. The pattern /d{3}[-.]?d{3}[-.]?d{4}/ matches US phone numbers in formats like 555-867-5309 or 555.867.5309. Regex engines are built into virtually every programming language and many command-line tools (grep, sed, awk), text editors (VS Code, Sublime Text), and databases (MySQL REGEXP, PostgreSQL ~).

Why regex testing requires a dedicated tool

Regex syntax has numerous subtle pitfalls: greedy vs. lazy quantifiers (.* vs. .*?), the difference between d and [0-9] in Unicode mode, zero-width assertions (lookahead (?=...) and lookbehind (?<=...)), and catastrophic backtracking in certain patterns. Writing a regex in your editor and then running it in code to see if it works is slow. A tester that shows matches in real time, highlights capture groups, and counts the number of matches lets you iterate in seconds.

Common regex use cases

Data validation: Email addresses, phone numbers, postal codes, IP addresses, credit card numbers, and custom formats all have well-defined regex patterns. Test yours against valid and invalid examples before deploying.

Text extraction: Pull specific fields out of log lines, extract all URLs from a document, or capture all dollar amounts from a financial report.

Find-and-replace: Advanced text editors support regex replacement with backreferences. Test the pattern before mass-replacing thousands of occurrences.

Log analysis: Server access logs, application logs, and security logs are line-oriented text. Regex is the standard way to filter, aggregate, and extract information from them.

Code refactoring: IDE find-and-replace with regex lets you rename patterns, reformat function call syntax, and migrate APIs across a codebase.

The UtilsGo Regex Tester runs all matching in your browser using JavaScript's native RegExp engine. Your test strings and patterns are never transmitted anywhere.