helmet

Helmet helps secure Express.js applications by setting various HTTP response headers that protect against common web vulnerabilities. It is a collection of smaller middleware functions that each set a specific security header. Helmet sets Content-Security-Policy to control which resources the browser is allowed to load, preventing cross-site scripting (XSS) and data injection attacks. It sets X-Content-Type-Options to prevent MIME type sniffing, Strict-Transport-Security to enforce HTTPS connections, X-Frame-Options to prevent clickjacking, and Referrer-Policy to control referrer information leakage. Helmet also removes the X-Powered-By header that identifies Express, reducing information disclosure to potential attackers. Each middleware function can be configured independently, and specific protections can be disabled if they conflict with application requirements. Helmet follows security best practices recommended by OWASP and is considered a baseline security measure for any Express application exposed to the internet. The library is lightweight and adds negligible performance overhead since it only modifies response headers. It is typically one of the first middleware applied in the Express middleware chain.