Cache-Control headers are present

Without Cache-Control headers, browsers fall back to heuristic caching — typically caching responses for 10% of their apparent age, or not at all. Every repeat visitor re-downloads content that hasn't changed, wasting bandwidth and adding latency on every navigation. Properly configured caching reduces server load, speeds up repeat visits, and improves CDN hit rates. ISO 25010 performance-efficiency identifies caching as a core mechanism for resource utilization. The absence of cache headers forces both browsers and CDNs into conservative or undefined behavior, leaving significant performance on the table.

Set Cache-Control explicitly on every response type. Match the directive to the content's mutability:

# Static assets (images, fonts, versioned JS/CSS)
add_header Cache-Control "public, max-age=31536000, immutable" always;

# HTML pages (content changes; revalidate)
add_header Cache-Control "public, max-age=3600, must-revalidate" always;

# Authenticated or personalized pages
add_header Cache-Control "private, no-store" always;

In Next.js API routes: res.setHeader('Cache-Control', 'public, max-age=3600, s-maxage=86400'). For app/ router, use export const revalidate = 3600 in route segments. Confirm with curl -sI https://yoursite.com | grep -i cache-control.