The Time To First Byte (TTFB) is the measurement between the transmission of the first request HTTP (initial request for a web page) by the browser and the beginning of the reception of the response, i.e. the reception of the first byte of data:

This time therefore represents the capacity of a website to produce and deliver the HTML code of the requested page quickly.

The optimisation of the TTFB is crucial because if there is a slowdown, this time will shifteverything else when the page is loaded. Indeed, as long as the HTML code is not received by the browser, it is impossible for it to load the elements that follow (javascripts, css, images...), therefore the Internet user will wait in front of a blank page.

Having the lowest possible TTFB is particularly important to ensure :

• a good user experience
• a good conversion rate
• good referencing (Google is particularly severe with pages with a high TTFB)

Finally, when TTFB is very long, it usually occurs because the web application does not use a full cache (e.g. Varnish, Full Page Cache, etc.). Therefore, the wait time is related to the time it takes the application to generate the page. This time also represents machine resources (typically CPU load) which can have an impact on :

• the cloud resources used
• the environmental impact of the application

In Quanta, the TTFB is visible in the synthetic analyses (the "User Paths".), but also in the Real User Monitoring.

The rating scale is as follows: