![]() However, if a website delivers the initial markup quickly, but that markup then requires JavaScript to populate it with meaningful content-as is the the case with Single Page Applications (SPAs)-then achieving the lowest possible TTFB is especially important so that the client-rendering of markup can occur sooner.Ĭonversely, a server-rendered site that does not require as much client-side work could have a higher TTFB, but better FCP and LCP values than an entirely client-rendered experience. A low TTFB is crucial for getting markup out to the client as soon as possible. Websites vary in how they deliver content. TTFB is not a Core Web Vitals metric, so it's not absolutely necessary that sites meet the "good" TTFB threshold, provided that it doesn't impede their ability to score well on the metrics that matter. As a rough guide, most sites should strive to have Time To First Byte of 0.8 seconds or less. What is a good TTFB score? #īecause TTFB precedes user-centric metrics such as First Contentful Paint (FCP) and Largest Contentful Paint (LCP), it's recommended that your server responds to navigation requests quickly enough so that the 75th percentile of users experience an FCP within the "good" threshold. Reducing latency in connection setup time and on the backend will contribute to a lower TTFB. Request, up until the point at which the first byte of the response has arrived.Service worker startup time (if applicable).TTFB is the sum of the following request phases: TTFB measures the elapsed time between startTime and responseStart. ![]() A diagram of network request phases and their associated timings. TTFB is a metric that measures the time between the request for a resource and when the first byte of a response begins to arrive. In the case of navigation requests-that is, requests for an HTML document-it precedes every other meaningful loading performance metric. It helps identify when a web server is too slow to respond to requests. Time to First Byte (TTFB) is a foundational metric for measuring connection setup time and web server responsiveness in both the lab and the field.
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