12/9/2023 0 Comments Timing diagram calculatorFor details, see the Google Developers Site Policies. How to improve TTFBĪn in-depth guide on optimizing TTFB has been published to give you more guidance on improving your website's TTFB.Įxcept as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. TTFB for cross-origin requests will not be measurable in the field if cross-origin servers fail to set a Timing-Allow-Origin header. It also accounts for the fact that some resources loaded from the primary origin may return a value of 0, since the connection is already open, or a resource is instantaneously retrieved from a cache. The above code snippet is similar to the one used to measure the TTFB for a navigation request, except instead of querying for 'navigation' entries, you query for 'resource' entries instead. The following example shows how to create a PerformanceObserver that listens for a navigation entry and logs it to the console: new PerformanceObserver((entryList) => `, entry.name) You can measure the TTFB of navigation requests in the browser with the Navigation Timing API. In the network panel of Chrome's DevTools.TTFB can be measured in the lab or in the field in the following ways. This is why the TTFB thresholds are a “rough guide”, and will need to be weighed against how your site delivers its core content. 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. 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.Ī diagram of network request phases and their associated timings. 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. Source Note: 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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