I built a network failure simulator in a single HTML file

Alex A. — Thu, 19 Mar 2026 14:13:53 +0000

I wanted a tool to run NOC failure drills without
setting up a lab. Everything I found was either
too heavy or required a server. So I built Simvex.

What it does

Simulates link failures and automatic rerouting
Connects to RIPE Atlas API for real latency data
ML anomaly detection (EMA Z-score + cooldown)
Load any topology via JSON
Export PDF reports, CSV, SVG, JSON topology
Zero install — single HTML file, open in browser

The interesting parts

Particles without re-creating DOM nodes
The traffic animation initially called remove()
and enter() every second. At scale it was slow.
Fixed by building the array once and only calling
.attr() on existing elements each step.

ML without spam
Raw Z-score on noisy latency data fires alerts
constantly. Added EMA smoothing (α=0.3) before
the Z-score calculation, plus a 5-step cooldown
between alerts. Alert spam dropped to zero.

Resize without rebuilding the map
Used ResizeObserver on the container — when size
changes, repositionSvg() recalculates W/H and
moves all SVG elements via .attr(). No rebuild.

Tech stack

Pure HTML/CSS/JS. D3.js for the network map.
Chart.js for latency history. jsPDF for reports.
No framework, no backend, no install.

Try it

https://simvex.gumroad.com/l/idxysp

Happy to answer questions about the implementation!

DEV Community: Alex A.

I built a network failure simulator in a single HTML file

What it does

The interesting parts

Tech stack

Try it