Flux Speed is a fully self-hosted network diagnostics tool. Every measurement runs
between your browser and this server — no third-party speed-test servers, no telemetry.
Below is what each section does and how to read it.
01 Running a Test
Press RUN SPEED TEST. The test runs four phases automatically:
latency baseline → download → upload → connection diagnostics. Use STOP to
abort at any time. The progress bar and phase label show what is happening.
02 Download & Upload Gauges
The dual gauges show live speed in Mbps. The needle and arc auto-scale to your
connection. Each gauge tracks PEAK, AVG (the honest
aggregate throughput) and SAMPLES.
- Warmup exclusion: the first 3 seconds of each direction are shown
live but excluded from the result, so TCP slow-start does not drag the number down.
- Parallel streams: 4–10 download / 3–8 upload connections run at once
to saturate fast links.
- Server-confirmed upload: upload speed counts only bytes the server
confirms it received — not bytes dumped into the OS buffer — so it is not inflated.
03 Latency, Jitter & Packet Loss
Shown in the center of the gauges.
Latency (ping) is the best round-trip time — lower is better.
Jitter is the variation between pings; high jitter causes choppy
calls. Packet loss is the percentage of probes that never returned.
04 Connection Diagnostics & Bufferbloat
This is the most useful panel for "my internet is fast but calls still lag" problems.
While the link is saturated, Flux Speed measures how much your latency increases under
load — this is bufferbloat.
- Overall quality score (0–100): a weighted blend of latency, jitter,
loss and bufferbloat.
- Bufferbloat grade (A+ → F): based on added latency under load.
A failing grade usually means enabling SQM / QoS (fq_codel or cake)
on your router will fix the lag — it is rarely an ISP speed problem.
- Findings: plain-language results with concrete next steps.
A+/A < 30 ms added — excellent
B/C 30–200 ms — noticeable lag during transfers
D/F > 200 ms — calls/gaming badly disrupted
05 Network Intelligence
Detected client IPv4/IPv6, ISP, reverse-DNS hostname, plus connection phase timings
(DNS, TCP, TLS, TTFB) and system info (CPU cores, memory, connection type). A missing or
broken IPv6 address is a common cause of mysterious slowdowns.
06 Network Trace
Two modes via the toggle:
- SERVER → CLIENT: a real hop-by-hop traceroute from the
server back to your IP, with per-hop latency and hostnames.
- CLIENT → SERVER: a connection-phase breakdown (DNS / TCP / TLS /
TTFB / RTT). Browsers cannot send raw traceroute packets, so this is the accurate
browser-feasible view of the forward path.
07 MTU, DNS & WebRTC
- MTU Discovery: finds the largest packet size that passes; below
1500 usually means VPN/tunnel overhead.
- DNS Leak Test: shows configured resolvers and resolution timing.
- WebRTC IP Detection: reveals local and public IPs your browser
would expose to any website.
08 Bandwidth History
Every completed test is saved in your browser (up to 50 entries) with timestamp, ping,
bufferbloat grade and download/upload bars. Use CLEAR to wipe it. Nothing
is sent anywhere — history lives only in your browser's local storage.
09 REST API
Everything here is also available programmatically at /api/v1/.
Interactive documentation is at /api-docs.html. Useful for scripted
monitoring or integrating Flux Speed into other tools.
10 Theme
Use the sun/moon button in the top bar to switch between the dark cyberpunk theme and a
light theme. Your choice is remembered on this device.