Effect-native, schema-first, completely type-safe state machines and statecharts, inspired by XState.

The goal of effect-machine is to become a core effect module.

It originates from the following PR.

import { Machine } from "@typeonce/effect-machine"
import { Effect } from "effect"
const Root = Machine.state({
  states: { Locked: {}, Unlocked: {} }
})
const Events = Machine.events({ Coin: {}, Push: {} })
const Turnstile = Machine.make({
  root: Root,
  events: Events
}).handle({
  initial: {
    target: "Locked"
  },
  states: {
    Locked: { on: { Coin: { target: "Unlocked" } } },
    Unlocked: { on: { Push: { target: "Locked" } } }
  }
})
const program = Effect.gen(function*() {
  const ref = yield* Machine.start(Turnstile)
  yield* ref.send(Events.Coin())
})

State and event schemas define the protocol. The root defines the topology and the handler tree adds behavior, and the result runs as an Effect-managed machine.

The workspace publishes four packages at the same version:

• @typeonce/effect-machine contains the machine runtime, testing modules, and documentation.
• @typeonce/effect-machine-react owns machine atoms in React without subscribing their owners to machine state.
• @typeonce/effect-machine-devtools contains the publishable local machine visualizer and CLI.
• @typeonce/oxlint-plugin-effect-machine checks Effect Machine models for common structural mistakes.

Install matching versions so the runtime, devtools, and lint rules stay aligned.

XState is the project's main inspiration and reference for statechart semantics and API coverage.

Direct API comparisons exposed gaps in Effect Machine, and benchmarks against XState drove many runtime performance improvements. effect-machine is not a direct XState replacement.