Jitter
Jitter is the variation in latency between consecutive packets. High jitter hurts calls and games even when the average ping looks fine.
What jitter is
If latency is how long packets take, jitter is how inconsistent that time is. Send ten pings and get round-trip times of 20, 21, 20, 22, and 20 ms, and the connection has almost no jitter. Get 20, 65, 18, 90, and 25 ms, and the average is similar but the jitter is high. Tools report it as the average difference between consecutive measurements or as the standard deviation of the samples; the exact formula varies, so compare values from the same tool.
Why it happens
Packets on the same path should take the same time, so jitter means something along the path is variable. The usual causes are queues: a router or a home Wi-Fi link that is near capacity holds packets for a changing amount of time depending on what else is in the queue. Wireless links add their own variability through retransmissions and channel contention. Cellular connections are jittery by nature. A congested proxy or VPN server adds jitter to every connection that passes through it, which makes it a useful quality measure for a proxy.
Why it matters
Applications that stream in real time, such as voice and video calls, online games, and remote desktops, cannot wait for late packets. They use a small buffer to absorb variation, and any packet that arrives later than the buffer allows is dropped, producing choppy audio, frozen video, or rubber-banding in a game. A connection with 30 ms latency and 40 ms jitter is worse for a call than one with 80 ms latency and 2 ms jitter. Web browsing and downloads, by contrast, tolerate jitter well because they can wait.
How to check
The ping tool sends a series of echo requests from our measurement node and reports the jitter alongside minimum, average, and maximum latency and packet loss. The speed test measures latency and jitter from your browser to our server, which includes your local network, your ISP, and any proxy or VPN in the path; run it with and without the tunnel to see how much the tunnel adds.
How to reduce it
Use a wired connection instead of Wi-Fi where possible, keep uploads from saturating the link while on a call, enable smart queue management on a router that supports it, and choose a proxy or VPN server that is close and not overloaded. For a proxy that is being evaluated for quality, consistent low jitter over several test runs at different times of day is a better sign than a single fast result.
A common misconception
Jitter is not packet loss. A jittery connection can deliver every packet; the problem is only when they arrive. Loss is reported separately and has different causes.