Web development and performance
What is Time to First Byte?
Time to First Byte measures how long from request to the first byte of the response arriving. It includes DNS, connection setup, TLS negotiation and server processing, and it is a constant added to every other loading metric.
Also called: TTFB · server response time
What a good number looks like
Under 200ms is good, under 500ms is acceptable, above 800ms is a problem that caps everything downstream. A static file from a CDN edge is typically tens of milliseconds; a slow shared host running a database query can be several hundred.
What actually causes a bad one
- A single origin server far from the visitor, with no CDN
- Server-side rendering with uncached database queries
- Shared hosting under load from other tenants
- Redirect chains, each adding a full round trip before the real response
- TLS negotiation on an old protocol version
Why it is often the cheapest fix
Moving a static site behind a CDN can remove several hundred milliseconds from every metric at once, for free on most platforms. That is a larger improvement than most front-end optimisation, and it takes an afternoon.
Where this is covered in depth
A definition can only go so far. Core Web Vitals, and the order that actually reduces them covers this properly — 3 minutes, free, no email required.
Who wrote this
Anas Bin Masud builds e-commerce sites and does technical SEO for businesses in the UK, Canada and Pakistan. These definitions come from client work rather than from a content brief — where an entry describes a mistake, it is usually one found on a real site. More about how I work.