5 API Security Headers You Should Use in 2026

5 API Security Headers You Should Use in 2026 Your API might be fast, scalable, and perfectly documented — but if you are missing these security headers, you are leaving clients exposed. As of February 2026, these five headers are essential for any production API: 1. Strict-Transport-Security (HSTS) Forces HTTPS connections. Simple, effective, non-negotiable. \ javascript // Express.js app.use((req, res, next) => { res.setHeader( "Strict-Transport-Security", "max-age=31536000; includeSubDomains" ); next(); }); \ \ What it prevents: Downgrade attacks, cookie hijacking. 2. Content-Security-Policy (CSP) Controls which resources can load. Critical for APIs serving HTML. \ javascript res.setHeader( "Content-Security-Policy", "default-src self; script-src self https://trusted.cdn.com" ); \ \ What it prevents: XSS, data injection attacks. 3. X-Content-Type-Options Stops browsers from sniffing MIME types. Forces them to respect your Content-Type. \ javascript res.setHeader("X-Content-Type-Opti