TTFB (Time to First Byte)
The time between the request leaving the browser and the first byte arriving from the server.
Analogy Mental model
How quickly the waiter acknowledges the order. The food takes as long as it takes, but the acknowledgement tells you the restaurant noticed.
In practice What you actually do
Under 600 milliseconds is the working target. The causes are almost always backend: uncached database queries, cold starts, no edge cache, overloaded shared hosting. Front-end work does nothing for this number.
Where people get burned Pitfalls
A slow first byte cannot be rescued by any amount of front-end optimisation, because everything else waits behind it. Teams rewrite templates for weeks while the origin takes four seconds to think.
This entry was written in English from the Chinese original, not machine-translated. Read the Chinese version →