A JSON-based serialization of SCXML (State Chart XML) for modern tooling, interoperability, and education.

Execution Engines

• Python engine: Deterministic trace emitter, vector generation, and compare tools. See docs/ENGINE-PY.md and py/ENGINE-PY-DETAILS.md.
• Ruby engine: Trace interface under active development with growing feature parity. See docs/ENGINE-RB.md.

JS/TS Harness (via SCION)

• The JS package ships a harness CLI scjson-scion-trace that directly requires scion-core to execute SCXML and emit JSONL traces. Install scion-core in your project to enable it.
• Supports both .scxml and .scjson input (the latter is converted to SCXML internally).
• Normalization flags: --leaf-only, --omit-delta, --omit-transitions, --strip-step0-noise, --strip-step0-states.
• Usage (package): npx scjson-scion-trace -I chart.(scxml|scjson) -e events.jsonl [--xml] [--leaf-only] [--omit-delta] [...]
• Dev alternative (in this repo): node tools/scion-runner/scion-trace.cjs -I chart.scxml -e events.jsonl --xml

scjson is a structured, schema-based representation of SCXML, the W3C standard for state machine modeling. This format preserves the semantics and hierarchy of SCXML while making it more accessible to modern tools, languages, and interfaces.

Why JSON?

• Easier to parse in JavaScript, Python, Rust, etc.
• Fits naturally with REST APIs, editors, and static validation
• Can be round-tripped to and from standard SCXML
• Works with compact formats like MessagePack or Protobuf when needed

• 💡 Interoperability: Serve as a bridge between SCXML and modern application ecosystems
• 📦 Portability: Enable translation to binary formats (MessagePack, Protobuf, etc.)
• 📚 Pedagogy: Make it easier to teach and learn state machines with cleaner syntax and visual tools
• 🔁 Round-trip Fidelity: Support conversion back to valid SCXML without semantic loss

The canonical scjson.schema.json file is located in /scjson.schema.json. It is generated from Pydantic models and used to validate all *.scjson documents. Detailed inference rules used by the converters are described in INFERENCE.md.

Each language implementation lives in its own directory, as a standalone module or library root:

/schema/ → JSON Schema definition of scjson /examples/ → SCXML and scjson sample pairs /tutorial/ → Git submodule: Zhornyak SCXML tutorial /python/ → Python reference implementation (CLI + library) /js/ → JavaScript CLI and library /ruby/ → Ruby CLI and gem /go/ → Go command line utility /rust/ → Rust command line utility /swift/ → Swift command line tool /java/ → Java command line tool /lua/ → Lua scripts /csharp/ → C# command line tool

Each directory is designed to be independently usable as a library or CLI tool.

See docs/COMPATIBILITY.md for the latest cross-language parity details and test notes.

This repo includes a curated set of canonical SCXML examples and their equivalent scjson forms in /examples. These are used for:

• Functional validation (SCXML ↔ scjson ↔ SCXML)
• Teaching state machine concepts via visual tools
• Demonstrating usage in editors, UI libraries, and low-code platforms

These examples are derived from and/or adapted from:

We include Alex Zhornyak’s SCXML Editor Tutorial as a Git submodule under /tutorial.
This provides a rich set of canonical SCXML test cases and diagrams.

Attribution is provided for educational purposes. No endorsement is implied.
Source: https://alexzhornyak.github.io/ScxmlEditor-Tutorial/

If you cloned this repo and /tutorial is empty, run:

git submodule init
git submodule update
Or clone with submodules in one step:

git clone --recurse-submodules https://github.com/your-org/scjson.git

This ensures you get the complete tutorial content alongside the examples and converters.

All converters share the same schema and test suite to ensure compatibility.

# Convert from SCXML to scjson
scjson convert --from scxml path/to/file.scxml --to scjson path/to/file.scjson

# Validate a scjson file
scjson validate path/to/file.scjson

pypi: [https://pypi.org/project/scjson/]

pip install scjson

npm: [https://www.npmjs.com/package/scjson]

npm install scjson
# harness requires scion-core
npm install scion-core

Harness (Node):

npx scjson-scion-trace -I path/to/chart.scxml -e events.jsonl --xml

rubygems: [https://rubygems.org/gems/scjson]

gem install scjson

RubyGems notes:

• Ruby CLI includes converters and a trace interface. See docs/ENGINE-RB.md for engine usage and maturity. The gem is published at the link above.

cargo: [https://crates.io/crates/scjson]

cargo install scjson

dockerhub: [https://hub.docker.com/r/iraa/scjson] (Full development environment for all supported languages)

docker pull iraa/scjson:latest

For a full example of installing toolchains and dependencies across languages see codex/startup.sh.

• User guide (Python engine): docs/ENGINE-PY.md
• Architecture & in-depth reference (Python): py/ENGINE-PY-DETAILS.md
• Compatibility matrix: docs/COMPATIBILITY.md
• Testing guide: TESTING.md
• Agents overview: AGENTS.md

Cross‑engine comparisons sometimes surface intentional, documented differences (e.g., ordering nuances, ECMA in semantics, history re‑entry). Use these resources to understand, normalize, and triage behavior across SCION (Node), Python, and Ruby:

• Comprehensive overview: docs/COMPATIBILITY.md
• Normalization profile: --norm scion in exec_compare sets leaf‑only, omit‑delta, omit‑transitions, strip‑step0‑states, and ordering=scion.
  • Example: python py/exec_compare.py tests/exec/toggle.scxml --events tests/exec/toggle.events.jsonl --reference "node tools/scion-runner/scion-trace.cjs" --norm scion
• CI known‑diffs list: scripts/ci_ruby_known_diffs.txt (used by scripts/ci_ruby_harness.sh --known to keep CI green while still reporting expected mismatches).
• Ruby converter in CI: when Nokogiri isn’t available, the Ruby CLI falls back to the Python converter for SCXML↔scjson only; execution remains Ruby. See docs/ENGINE-RB.md (CI Notes).

cd py
pip install -r requirements.txt
pytest -q

cd js
npm ci
npm test --silent

cd ruby
gem install bundler
bundle install
bundle exec rspec

cd go
go test ./...
go build

cd rust
cargo test

cd swift
swift test

cd csharp
dotnet test -v minimal

cd lua
luarocks install luaexpat --deps-mode=one
luarocks install dkjson --deps-mode=one
luarocks install busted --deps-mode=one
busted tests

All source code in this directory is released under the BSD 1-Clause license. See LICENSE and LEGAL.md for details. Additional documentation is available in AGENTS.md and TESTING.md.