Why is the first request to a site slower than the next?
The first visit pays for DNS resolution, a TCP connection, and a TLS handshake before any HTTP byte moves. Later requests reuse cached DNS answers and often an open connection, so they skip most of that setup. That is why connection reuse and preconnect hints help real-world load times.
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From Enter Key to Pixels: What Happens When You Type a URLDNS caches, TCP, TLS, HTTP, then HTML parsing, the render tree, layout and paint. Every stage is a place a page can be slow, and a place to fix it.
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