A regular expression (often abbreviated as regex or regexp) is a sequence of characters that forms a search pattern. It provides a concise, formal language to locate, extract, validate, or replace patterns within strings across virtually every modern programming language, including JavaScript, TypeScript, Python, Go, and Rust.

Unlike static substring lookups, regular expressions describe complex syntax rules using character classes, quantifiers, lookaheads, and capture groups. Whether validating email addresses, extracting dates from logs, or sanitizing user inputs, regular expressions are essential everyday developer tools.

This Regex Toolkit is designed for rapid iteration with zero latency:

In JavaScript and TypeScript, regular expressions are instances of the built-in RegExp object. You can create them using literal notation or the constructor:

// 1. RegExp literal (compiled at evaluation time)
const emailRegex = /^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$/i;

// 2. Testing boolean match
const isValid = emailRegex.test("developer@example.com"); // true

// 3. Extracting all matches with groups (ES2020+)
const text = "item 42 and item 99";
const matches = [...text.matchAll(/item (\d+)/g)];
for (const match of matches) {
  console.log(match[0], match[1]); // "item 42", "42"
}

// 4. Replacing with backreferences
const formatted = "2026-09-03".replace(/(\d{4})-(\d{2})-(\d{2})/, "$2/$3/$1");
// formatted === "09/03/2026"