Files and schemas

Application data directory

~/Library/Application Support/molt/

File	Owner	Format	Created when
config.toml	Rust configuration layer	TOML	First configuration load when missing, or Settings save
notebooks.json	React persistence hook through Rust file commands	Compact JSON	First persistable notebook change after load

The code falls back to a relative working-directory path only if the operating system configuration directory cannot be resolved.

Notebook schema version 1

A representative file is:

notebooks.json

{
  "version": 1,
  "tabs": [
    {
      "tabIndex": 0,
      "cells": [
        {
          "id": "0f4a9e9a-72de-4b04-a180-56e0c44fbf05",
          "type": "code",
          "source": "value = 21\nvalue * 2"
        }
      ]
    },
    {
      "tabIndex": 1,
      "cells": [
        {
          "id": "1ec4e25e-81e4-4b44-8429-07ff095e8052",
          "type": "code",
          "source": ""
        }
      ]
    },
    {
      "tabIndex": 2,
      "cells": [
        {
          "id": "97f8ef11-6248-4cd8-bc4f-e1386ec69cc0",
          "type": "code",
          "source": ""
        }
      ]
    },
    {
      "tabIndex": 3,
      "cells": [
        {
          "id": "9b87faef-1524-4f13-b64d-8a0cf4701303",
          "type": "code",
          "source": ""
        }
      ]
    }
  ]
}

Field reference

Field	Type	Meaning	Validation on load
version	Number	Persistence format marker; writer emits 1	Must equal 1
tabs	Array	Persisted tab entries	Must be an array
tabIndex	Number	Matches frontend notebook index	Unique integer from 0 through 3
cells	Array	Ordered cell records	Empty array is replaced with one fresh code cell
id	String	Stable cell identity, normally a browser-generated UUID	Nonempty and unique across all tabs
type	code or markdown	Reserved cell kind	Restored, but UI still renders a Python editor
source	String	Raw Python source	Restored verbatim

Fields not stored

The writer strips:

• executionCount
• outputs
• state
• Notebook kernelState
• Notebook executionCounter
• Global activeTab
• Focus and command-mode state

Load behavior

1. Rust returns the file contents as a JSON string or null when missing.
2. The React hook parses the string.
3. The frontend validates the version, tabs, indices, cells, IDs, types, and sources.
4. Valid matching tabs replace their cell arrays.
5. Each restored cell receives executionCount: null, outputs: [], and state: "idle".
6. Existing notebook kernel and execution-counter defaults remain.
7. The just-loaded persistable snapshot is remembered to prevent an immediate no-op rewrite.

If reading or validation fails, Molt shows a warning and disables autosave so the existing file is not overwritten with defaults.

Write behavior

• The JSON is serialized compactly with JSON.stringify.
• Writes occur after a 1.5-second debounce.
• Identical persistable snapshots are skipped.
• Saves are serialized so older writes cannot finish after newer ones.
• Rust creates the directory if necessary and atomically replaces the file through a temporary file.
• A pending write is attempted during frontend unmount but cannot be awaited there.

There is no cross-process file lock, backup rotation, or built-in history. Avoid concurrent manual edits.