SPDY (pronounced speedy) is an open networking protocol developed primarily at Google for transporting web content. SPDY manipulates HTTP traffic, with particular goals of reducing web page load latency and improving web security. The name "SPDY" is a trademark of Google.

  • SPDY allows client and server to compress request and response headers, which cuts down on bandwidth usage when the similar headers (e.g. cookies) are sent over and over for multiple requests.
  • SPDY allows multiple, simultaneously multiplexed requests over a single connection, saving on round trips between client and server, and preventing low-priority resources from blocking higher-priority requests.
  • SPDY allows the server to actively push resources to the client that it knows the client will need (e.g. JavaScript and CSS files) without waiting for the client to request them, allowing the server to make efficient use of unutilized bandwidth.

SPDY requires the use of SSL/TLS (with TLS extension ALPN), and does not support operation over plain TCP. The requirement for SSL is for security and to avoid incompatibility when communication is across a proxy.