fateA statechart engine for Go

Hierarchical, parallel, deterministic, persistable. The full Harel statechart feature set — with zero dependencies.

Real statecharts, not flat FSMs

Hierarchical (compound) states, parallel regions, and deep/shallow history — the Harel model, inspired by SCXML and XState v5, expressed idiomatically in Go generics.

See the concepts

Zero dependencies

The engine imports only the standard library. The optional Temporal integration lives in a separate module, so you never pull in the Temporal SDK unless you ask for it.

Install

Deterministic & persistable

A Machine is immutable and shareable; an Actor's state serialises to JSON and restores byte-for-byte. Safe to drive from deterministic runtimes like Temporal workflows.

How it works

Effects as data

Delayed (after) transitions and invoked/spawned child machines are surfaced as pending effects. Your adapter performs them — the engine just computes the next state.

The effect model

Visualise & diff

Render any machine to ASCII, Mermaid, or a graph JSON. Inspect and diff statecharts from the command line with the engine-only fate CLI.

Examples

Live studio

fate-studio renders and drives any fate machine in the browser — a chart viewer and live simulator. A separate project, so the engine stays dependency-free.

About the studio