Guide
Understanding TTFB
Time to First Byte measures how long it takes before the browser receives the first byte of the response. It can be a useful hosting signal, but only when interpreted with context.
Useful signal
What TTFB can suggest
Repeated high TTFB on lightweight HTML can point toward server processing, origin location, cache misses, overloaded resources, or provider limits.
Limit
What TTFB cannot prove alone
It cannot identify a hidden origin host behind a CDN, and it does not explain layout shifts, heavy JavaScript, oversized images, or slow third-party scripts.
Responsible use
Pair it with context
Pair TTFB with response headers, cache status, page weight, repeat tests, and field data when available. If sources disagree, lower confidence.
| TTFB pattern | Context | Interpretation |
|---|---|---|
| 150 ms median | Large scripts delay interaction | Do website work first |
| 1,200 ms median | Small page, few requests, repeatable pattern | Investigate origin response and hosting constraints |
| Mixed 180 ms and timeout results | One source failed | Treat as insufficient evidence until retested |