There is a correlation between lower time-to-first-byte (TTFB) metrics and higher search engine rankings. Websites with servers and back-end infrastructure that could quickly deliver web content had a higher search ranking than those that were slower. This means that, despite conventional wisdom, it is back-end website performance and not front-end website performance that directly impacts a website's search engine ranking. The question is, why?
TTFB is likely the quickest and easiest metric for Google to capture. Google's various crawlers will all be able to take this measurement. Collecting document complete or fully rendered times requires a full browser. Additionally, document complete and fully rendered times depend almost as much on the capabilities of the browser loading the page as they do on the design, structure, and content of the website. Using TTFB to determine the "performance" or "speed" could perhaps be explainable by the increased time and effort required to capture such data from the Google crawler. We suspect over time, though, that page rendering time will also factor into rankings due to the high indication of the importance of user experience.
TTFB is easy to calculate and is a reasonable metric to gauge the performance of an entire site. TTFB is affected by 3 factors:
The network latency between a visitor and the server.
How heavily loaded the web server is.
How quickly the website's back end can generate the content.
Websites can lower network latency by utilizing Content Distribution Networks (CDNs). CDNs can quickly deliver content to all visitors, often regardless of geographic location, in a greatly accelerated manner. Of course, the very reason these websites are ranked so highly could be the reason they need to have high capacity servers, or utilize CDNs, or optimize their application or database layers.
The back-end performance of a website directly impacts search engine ranking. The back end includes the web servers, their network connections, the use of CDNs, and the back-end application and database servers. Website owners should explore ways to improve their TTFB. This includes using CDNs, optimizing your application code, optimizing database queries, and ensuring you have fast and responsive web servers. Start by measuring your TTFB with a tool like WebPageTest, as well as the TTFB of your competitors, to see how you need to improve.
Practice Head (QA / Software Testing)