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Getting Started

Requirements

  • Python 3.10 or later
  • Node.js 18 or later (for the visual editor)

1. Install the backend

pip install moldo

git clone https://github.com/GracePeterMutiibwa/moldo
cd moldo
python3 -m venv .venv
source .venv/bin/activate   # Windows: .venv\Scripts\activate
pip install -e .

2. Start the backend server

moldo --serve

You should see:

INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Confirm it is healthy:

curl http://127.0.0.1:8000/health
# → {"status":"ok"}

3. Open the editor

Download and open mflow-editor from the releases page.

Or run it from source:

git clone https://github.com/GracePeterMutiibwa/mflow-editor
cd mflow-editor
npm install
npm start

The toolbar shows a green dot when the editor has successfully connected to your backend.

4. Build your first program

Let's print the numbers 1 to 5.

  1. In the sidebar, expand Variables and drag a Declare Variable block onto the canvas. Set name = i, type = int, value = 1.
  2. Expand Control and drag a While Loop block. Set left = @i, op = <=, right = 5.
  3. Expand I/O and drag a Print block. Set value = @i. Connect it as the loop body.
  4. Expand Variables and drag a Modify Variable block. Set name = @i, op = +, operand = 1. Connect it after Print inside the loop body.
  5. Press Run.

The output panel shows:

1
2
3
4
5

Compile a flow to Python

After building a program in the editor, export it from File > Export and compile it from the terminal:

moldo myprogram.json            # print generated Python to stdout
moldo -c myprogram.json -o myprogram.py   # write to a file
python myprogram.py             # run it standalone

See the CLI Reference for all options.

Development mode

Run the backend with auto-reload (restarts on file changes):

moldo --serve --reload

Run the editor with the Node.js inspector:

npm run dev

Troubleshooting

Editor shows red dot / "backend offline" : The backend is not running or not reachable at http://127.0.0.1:8000. Check that moldo serve is running and that no firewall is blocking localhost.

ModuleNotFoundError: No module named 'moldo' : Run pip install -e . inside the moldo directory (with your virtualenv active).

Port 8000 already in use : uvicorn moldo.api.server:app --port 8001 and update const BACKEND in index.html to match.