Slowest requests with HAR Desk
This opens a made-up slow page: a 1.9 second document, a 2.4 MB script, a large image and a search call that spends three seconds waiting. The slow-only filter is on, and each request has its waterfall bar.
- Load the HAR and read the cards: duration, 95th percentile and the Slowest and Largest lists.
- Turn on Slow only (1 s and above) to hide everything fast.
- Click a row and open Timing to see blocked, DNS, connect, send, waiting and receive.
- Tick Third party to see whether analytics, fonts or ads are the slow ones.
What to know
Total time is a poor guide on its own. The split matters: a long Waiting (time to first byte) means the server was slow, a long Receive on a large body means the payload is the problem, a long Blocked often means the browser was limited to six connections per host or was waiting for something earlier, and DNS or Connect time on the first request to a host is normal and happens once.
The waterfall places each request on the capture timeline using its start time, so you can see what ran in parallel and what waited. Colours are blocked, DNS and connect, send, waiting for the first byte and receive. TLS time is part of connect in the HAR format and is not drawn twice. Timings a file does not provide are shown as a single bar for the total.
The 95th percentile and average are computed over the requests currently in the file, not over a real-user population. A single capture is a sample from one machine and one network; use it to find the obvious outliers, then confirm with several recordings before you decide it is a regression.
Updated · Cosmovex
Questions
What does Waiting mean?
It is the time between sending the request and receiving the first byte of the response, usually the server's processing time plus network latency to it.
Why is a request marked third party?
Its registrable domain differs from that of the first page in the capture. This is an approximation using the last two labels of the host, not the public suffix list.
Does the size shown include headers?
It is the transferred size when the browser recorded one, otherwise body size plus headers, otherwise the decoded content size.
Can I export the slowest requests?
The support pack lists the five slowest and five largest requests along with failures and hosts.
The free plan covers everything on this page. HAR Desk Pro ($29, paid once) is described on the HAR Desk page.
