Time to First Byte
The interval between a navigation request starting and the first byte of the response arriving; a foundational input to LCP and a signal…
TechnicalContent-Encoding
Compression (gzip, Brotli, Zstandard)
Encoding text responses to reduce transfer size; Brotli typically beats gzip on HTML, CSS and JavaScript, with Zstandard now also supported by browsers.
In full
Compression is negotiated via `Accept-Encoding` and `Content-Encoding` headers and applies to text formats; already-compressed formats such as WebP, AVIF and WOFF2 should not be re-compressed. Static assets can use maximum Brotli levels at build time, while dynamic HTML uses a lower level to keep CPU cost down. Missing compression on HTML is one of the fastest wins in any technical audit.
Example
Enabling Brotli reduces a 180 KB HTML document to 22 KB over the wire.
Related terms
Cache-Control
The HTTP header governing how browsers, CDNs and proxies store and revalidate a response, using directives such as max-age, s-maxage and…
Content Delivery Network
A distributed network of edge servers that caches and serves content close to users, reducing latency and offloading the origin.
Largest Contentful Paint
A Core Web Vital measuring the render time of the largest image, video poster or text block visible in the viewport; good is 2.5 s or less…
HTTP/2
A binary, multiplexed version of HTTP that carries many concurrent requests over one TCP connection with header compression.