AltF NetCheck
Bufferbloat Test
This bufferbloat test measures your ping while the connection is idle and again while it is fully loaded by the download and upload tests, then grades the increase from A+ (under 5 ms) to F (over 400 ms). A high grade means calls and games stay smooth even when someone else is streaming or downloading on the same line.
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- Ping, jitter and bufferbloat
- History stays on your device
Run the internet speed test
-Mbps
-Mbps
-ms
Idle round-trip time
-ms
Ping variation
-ms
Measured during download and upload
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Grade A+ to F
Your connection
Run a test to see your ISP, public IP (masked by default), approximate location and the server you were tested against.
The test talks to Cloudflare's speed-test servers, which see your IP address like any website does. AltFTool does not store your results; history stays in this browser.
Your speed history
Every test you run is saved here, in this browser only, so you can compare times of day, rooms or Wi-Fi vs cable. Nothing is uploaded.
What is bufferbloat?
Routers and modems hold packets in a queue when the line is full. When those queues are too large, every new packet waits behind hundreds of others, so latency climbs from tens to hundreds of milliseconds. Speed tests that only measure idle ping miss it entirely, which is why a connection can test fast and still lag on calls.
Grades
- A+: under 5 ms increase. No measurable bufferbloat.
- A: under 30 ms. Excellent for gaming and calls under load.
- B: under 60 ms. Good; occasional lag in fast games.
- C: under 200 ms. Calls stutter when the line is busy.
- D: under 400 ms. Heavy lag whenever anyone downloads.
- F: 400 ms or more. Severe; the line is unusable for real-time apps while busy.
How to fix bufferbloat
- Turn on Smart Queue Management (SQM) with fq_codel or CAKE; many routers call it QoS, Adaptive QoS or Smart Queue.
- Set the SQM limits to about 85-95% of the speeds this test measures.
- Routers running OpenWrt, and many mesh systems, support SQM out of the box.
- If your ISP router has no such option, put your own router behind it in bridge mode.
- Run this test again afterwards: the grade should jump to A or A+.
Bufferbloat Test FAQ
How is bufferbloat measured?
Ping keeps running in the background during the download and upload tests. The grade is based on how far the higher of those two loaded medians rises above your idle ping.
Does bufferbloat affect download speed?
Not much. It affects responsiveness: games, calls and even page loads feel slow while the line is busy, although the Mbps figure stays high.
Will a faster plan fix bufferbloat?
Rarely. The queue just fills at a higher rate. SQM on the router is the reliable fix, and it costs only a small fraction of peak speed.
Want the complete picture? The main page explains every result, how much speed each activity needs, why tests read lower than your plan and how NetCheck measures.
Internet speed test guideAltFTool stores no results and no IP addresses. Tests run against Cloudflare's speed-test servers; your history is kept in this browser only.