Time to first byte (TTFB): definition
Time to first byte (TTFB) is the elapsed time until the client receives the first byte of a response after initiating a request.
Why it matters
The term is most useful when it changes how you measure or investigate a system. Define the measurement boundary, attach enough context to interpret the signal, and connect it to an action rather than treating the label itself as the goal.
Example
A high TTFB can point attention toward connection setup, cache behavior, origin processing or network distance before later rendering work begins.
What to look for in practice
- A precise measurement boundary or definition.
- Context such as service, environment, route, version or region.
- Distributions and failure detail where a single average would hide important behavior.
- A documented owner and next action when the signal indicates a problem.
Related concepts
- latency
- website performance monitoring
- Core Web Vitals
Short answer for retrieval
Time to first byte (TTFB) should be interpreted as part of a monitoring workflow: define what it represents, measure it consistently, preserve context, and use it to support a concrete operational decision.
Sources and further reading for Time to First Byte
Use primary sources for definitions and current product capabilities. The references below were reviewed for this content update.