Introduction

Synapse Arch is an architecture framework for Kotlin and Jetpack Compose that eliminates cross-feature coordination as a concern. Every component is an isolated state machine with typed inputs and outputs. Components never hold references to each other — they communicate exclusively through a central bus called the SwitchBoard.

The coordination problem

Most architectures accumulate coordination code as a feature grows. ViewModel A needs to know about ViewModel B. A new checkout screen needs to react to a session timeout that originally lived inside auth. Over time, the graph of “who-calls-who” becomes the architecture itself, and every new feature requires wiring into every relevant existing feature.

The result: adding a feature is not additive. It changes existing features. Tests multiply. Refactors become risky. Correctness becomes a property of the whole graph, not the individual pieces.

How Synapse solves it

Synapse enforces that components only communicate through typed messages (impulses) dispatched on the SwitchBoard. A component declares the impulses it emits and the impulses it consumes. That’s its entire contract with the rest of the app.

Because components share only impulse types:

• Adding Feature B never requires modifying Feature A. If B wants to react to something A already emits, it subscribes to that impulse type. A doesn’t know B exists.
• Cross-cutting concerns become interceptors. Auth, analytics, logging, session management — all of these are composable middleware that runs on the bus, not wiring threaded through feature code.
• Testing is real-bus, no mocks. The SwitchBoard is the same in tests as in production. You verify behavior by observing what impulses a component emits given a sequence of inputs.

This gives you a property most architectures can’t: compositional correctness. If Component A works through the SwitchBoard and Component B works through the SwitchBoard, then A + B works — because the bus is real and the type system enforces the contract.

Three channels

The SwitchBoard routes three kinds of traffic:

Channel	Replay	Use for
State	1	Persistent state streams — new subscribers get the latest value
Reaction	0	Fire-and-forget events — only active collectors receive them
Request	1	Data fetching via Providers — full Loading / Success / Error lifecycle

Each channel has upstream and downstream interceptor slots, so cross-cutting concerns slot in at a well-defined place. You’ll see these throughout the docs; each gets a dedicated page later.

No ViewModels

Synapse replaces the ViewModel entirely.

• Compose screens use the Node / CreateContext DSL. Node holds screen-local state; CreateContext provides shared services without prop drilling.
• Non-Compose contexts — services, background work, non-Compose UI — use Coordinator, which gives you the same bus access outside a composable body.
• Data fetching is handled by Providers wired automatically via KSP. Plug into Hilt or Koin and providers are registered at build time.

Next

Continue to Installation to add Synapse Arch to your project.