5 Essential API Security Headers Every Developer Should Know

Security Headers Are Your First Line of Defense Security headers are your API's first line of defense. As of February 2026, proper header configuration can block most common attacks before they reach your application logic. 1. Strict-Transport-Security (HSTS) Forces HTTPS connections. Without this, attackers can intercept traffic on insecure networks. // Express example app . use (( req , res , next ) => { res . setHeader ( ' Strict-Transport-Security ' , ' max-age=31536000; includeSubDomains ' ); next (); }); Best practice: Set max-age to at least 1 year (31536000 seconds). 2. Content-Security-Policy (CSP) Controls which resources can be loaded. Prevents XSS by blocking inline scripts. res . setHeader ( ' Content-Security-Policy ' , " default-src 'self'; script-src 'self' https://trusted.cdn.com " ); 3. X-Content-Type-Options Stops browsers from MIME-sniffing responses. Prevents execution of malicious files. res . setHeader ( ' X-Content-Type-Options ' , ' nosniff ' ); 4. X-Frame-Opti