Time to first byte — What is it? Why does it matter?
Harry Roberts writing on CSS Wizardry:
One metric I feel that front-end developers overlook all too quickly is Time to First Byte (TTFB). This is understandable—forgivable, almost—when you consider that TTFB begins to move into back-end territory, but if I was to sum up the problem as succinctly as possible, I’d say: While a good TTFB doesn’t necessarily mean you will have a fast website, a bad TTFB almost certainly guarantees a slow one.
Even though, as a front-end developer, you might not be in the position to make improvements to TTFB yourself, it’s important to know that any problems with a high TTFB will leave you on the back foot, and any efforts you make to optimises images, clear the critical path, and asynchronously load your webfonts will all be made in the spirit of playing catchup.