The fate CLI

cmd/fate is a small command-line tool that renders, inspects, and diffs statecharts. It works on JSON files rather than on Go code, so it is not tied to any particular set of machines.

go install github.com/arisros/fate/cmd/fate@latest

Released binaries for Linux and macOS are also attached to each GitHub release.

Input formats

The tool reads two kinds of JSON:

• A machine descriptor — the JSON of describe.MachineDescriptor, as produced by Machine.Describe and marshalled, or served by a studio at /m/{name}/describe.
• A persisted snapshot — the JSON written by Actor.Persist.

A path of - reads from standard input, so the tool composes with anything that can print a descriptor.

Commands

Command	Input	Output
fate render <descriptor.json|->	descriptor	ASCII state diagram
fate mermaid <descriptor.json|->	descriptor	Mermaid stateDiagram-v2 source
fate graph <descriptor.json|->	descriptor	resolved node/edge graph as JSON
fate snap <snapshot.json|->	snapshot	a readable view of a persisted snapshot
fate diff <left.json> <right.json>	two snapshots	structural diff

Examples

Render a descriptor produced by your own program:

go run ./cmd/describe-my-machine | fate render -

Generate Mermaid source and embed it in a document:

fate mermaid machine.json > docs/machine.mmd

Compare two persisted snapshots, for example before and after an event:

fate diff before.json after.json

Related

• Effects and adapters — what a snapshot contains beyond the active configuration.
• Persistence and determinism — the snapshot format and its guarantees.
• fate-studio — the same rendering, in the browser, with a live simulator.