Time to First Byte (TTFB)
The duration from the user's request to the first byte of the server response reaching the browser. TTFB measures server-side processing speed and network latency, directly impacting all subsequent loading metrics.
TTFB is the foundational performance metric because every subsequent metric depends on it. A slow TTFB delays LCP, FCP, and ultimately INP because the page cannot be interactive until content arrives. TTFB includes DNS lookup, TCP connection, TLS handshake, server processing time, and the network transit of the first response byte.
For engineering teams, TTFB optimization focuses on reducing server processing time and leveraging edge infrastructure. Key strategies include CDN deployment to reduce geographic latency, server-side caching to avoid redundant computation, database query optimization, HTTP/2 or HTTP/3 for connection efficiency, and early hints (103 status code) to allow browsers to preload resources while the server is still processing. For dynamic pages, consider stale-while-revalidate caching patterns that serve cached content immediately while refreshing in the background. Google considers TTFB of 800ms or less as good. For static sites and ISR pages, TTFB should be under 200ms from edge nodes.
Related Terms
Core Web Vitals
A set of three Google-defined metrics that measure real-world user experience for loading performance, interactivity, and visual stability. Core Web Vitals are a confirmed ranking factor in Google Search.
Largest Contentful Paint (LCP)
A Core Web Vital that measures the time from page load start until the largest visible content element (image, video, or text block) is rendered on screen. Good LCP is 2.5 seconds or less.
Interaction to Next Paint (INP)
A Core Web Vital that measures the latency of all user interactions (clicks, taps, keyboard input) throughout the page lifecycle, reporting the worst interaction. Good INP is 200 milliseconds or less.
Cumulative Layout Shift (CLS)
A Core Web Vital that measures the total amount of unexpected layout shifts that occur during a page's entire lifespan. Good CLS is 0.1 or less, where layout shifts are calculated from the impact and distance of moving elements.
Crawl Budget
The number of pages a search engine bot will crawl on your site within a given timeframe, determined by crawl rate limit and crawl demand. Crawl budget optimization ensures important pages are discovered and indexed efficiently.
Canonical URL
An HTML element that tells search engines which version of a page is the preferred one when multiple URLs serve similar or identical content. Canonical tags consolidate ranking signals and prevent duplicate content issues.