Regex Tester online

Regular expressions (regex) are patterns used to match character combinations in strings. They are used in almost every programming language and are invaluable for text processing, validation, search, and replace operations.

What is a Regex Tester and How Does It Work Online?

A regular expression (regex) is a sequence of characters that defines a search pattern. This online regex tester lets you write a pattern in the first field, paste your test string in the second, and immediately see all matches highlighted — no need to write boilerplate code or open a terminal. It uses JavaScript's native RegExp engine running entirely in your browser, so your patterns and data never leave your device.

Common Regex Patterns and What They Do

• Email validation: ^[\w.-]+@[\w.-]+\.[a-z]{2,}$ — matches most standard email addresses
• URL matching: https?:\/\/[\w\-._~:\/?#\[\]@!$&'()*+,;=]+ — matches http and https URLs
• IP address (IPv4): \b(\d{1,3}\.){3}\d{1,3}\b — matches four dot-separated octets
• Phone number (US): \(\d{3}\)\s?\d{3}-\d{4} — matches (555) 867-5309 format
• Hex colour: #([0-9a-fA-F]{3}|[0-9a-fA-F]{6})\b — matches #fff and #ff5733
• Digits only: ^\d+$ — matches strings that contain only numbers
• Non-empty line: ^(?!\s*$).+ — matches any line that isn't blank or whitespace-only

Regex Flags Explained

Flags modify how the regex engine interprets the pattern. The most common flags used in JavaScript are:

• g (global) — find all matches, not just the first one
• i (case-insensitive) — treat uppercase and lowercase as equivalent
• m (multiline) — make ^ and $ match the start/end of each line, not just the whole string
• s (dotAll) — make the dot (.) match newline characters too
• u (unicode) — enable full Unicode matching for emoji and international characters

Who Uses a Regex Tester?

Developers reach for a regex tester whenever they need to validate input fields, scrape structured data from text, write log-parsing scripts, or clean up messy datasets. QA engineers use regex to filter test output. Data analysts use it to extract fields from unstructured text files. Writers and editors use it in find-and-replace workflows. If you work with text — in any language, on any platform — regex is one of the most transferable skills you can have.