System Coupling: Change Propagation & Blast Radius

System Architecture

Modules 18

Topology

Coupling strength 45%

Cascade decay per hop 80%

Click a module, or press "Trigger change", to inject a change and watch it propagate.

Cascade Readouts

Blast radius

0 / 0 (0%)

Max depth

0 hops

Edges fired

Avg coupling

0.00

How it works

Every module in the graph is a node; a directed edge A→B means "B depends on A" with a coupling weight w ∈ (0,1) — how strongly a change in A is felt by B. Triggering a change runs a stochastic breadth-first cascade from one source module:

P(propagate along edge, depth d) = w · decay^d
each edge is an independent Bernoulli trial at that probability

A module only fires once per cascade even if reached via several paths (its trigger probability is evaluated the first time it is reached, at its shallowest depth). The blast radius is the fraction of the whole system that ends up changed; max depth is the longest chain of dependent changes the cascade reached before decay drove every remaining edge's probability to effectively zero.

Coupling strength — scales every edge weight w up or down together. High coupling means a local edit anywhere tends to ripple across most of the system; low coupling keeps changes contained to a module's immediate neighbours.
Cascade decay — how much propagation probability is lost per hop of distance from the original change. A decay near 100% lets a strong signal travel arbitrarily far; a low decay snuffs it out within one or two hops regardless of coupling.
Topology — Layered pipeline arranges modules in stages with mostly forward edges (like a request pipeline); Dense mesh gives every module several cross-cutting dependencies (like a poorly-isolated monolith), which is why the same coupling value produces a much larger blast radius there.

This is the same mathematical shape architects use informally when they talk about "blast radius" or "change amplification": low coupling and shallow dependency chains are what make a system safe to modify one piece at a time.

Untouched module Change source Affected by cascade

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