OM Core for VS Code

A grid GUI for OM Core, a multidimensional modeling engine (dimensions, cubes, rules, views), inside VS Code.

Preview. This is an early version. Only the core workflow works: open a model, browse it, edit values and see the results recalculate, save. Everything else is visible but disabled (see Not available in this preview).

The extension is only the interface. The engine (om-core, Python) runs as a separate local process, and you install it once, as described below.

Requirements

VS Code 1.80 or newer
Git
uv, which manages Python for om-core. It downloads the Python version om-core needs (3.12 or newer), so you do not need to install Python yourself.

Install

1. Install uv

Windows (PowerShell):

powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

macOS / Linux:

curl -LsSf https://astral.sh/uv/install.sh | sh

Open a new terminal and check that it works: uv --version prints a version.

Then close all VS Code windows and start VS Code again. VS Code only picks up the new PATH when it starts; Reload Window is not enough.

2. Get the engine

In a terminal, go to the folder where you want the engine to live (for example your home folder), then run:

git clone https://github.com/cloudcell/om-core.git
cd om-core
git checkout 72a90ca
uv sync

This creates an om-core folder there, for example C:\Users\you\om-core on Windows or /home/you/om-core on Linux. Remember it: step 4 needs it.
git checkout 72a90ca is the om-core version this extension was tested with. Newer versions may work, but are not checked.
Do not skip uv sync. It downloads the dependencies (several hundred MB, a few minutes the first time). If it has not been run, the first start of the runtime takes longer than the extension waits (20 seconds) and fails.

3. Install the extension

Download om-tools-<version>.vsix from the Releases page, then in VS Code: Extensions panel → … menu (top right of the panel) → Install from VSIX… → choose the file.

Or from a terminal, in the folder with the downloaded file:

code --install-extension om-tools-<version>.vsix

(On macOS, code works in a terminal only after Shell Command: Install 'code' command in PATH in the VS Code command palette.)

4. Point the extension at the engine

Click the OM Core icon in the activity bar (the left edge of the window). In the side panel, press Settings, then click Choose folder… above the Om Core: Om Core Path setting and choose the om-core folder from step 2 (the one that contains main.py).

You can also skip this step: when the setting is empty, Start Runtime asks for the folder once and saves it. Or type the path into the setting yourself, or put it in settings.json:

"omCore.omCorePath": "path/to/om-core"

5. Check that everything is ready

The OM Core side panel shows one row per part the engine needs. Before the first start it should look like this:

Row	Should show
Runtime	`Not running` (it is started in the quick start below)
GUI	`Not open`
Engine path	the folder from step 2, green
Dependencies	`.venv found`, green
uv	the path to `uv`, green

A row that is not green says what is wrong; hover over it for details. See also Troubleshooting.

Quick start: a five-year financial model

The om-core folder you cloned in step 2 comes with example models in its examples folder. This one is a five-year model of a fictional company (NZ Gadgets & Widgets), with views for drivers, profit and loss, balance sheet, cash flow and valuation. The statements are calculated by rules from the drivers, so changing a driver changes the results.

The menus and panels in the steps below (File, Model Browser, Calculation Flow) are inside the OM Core tab, not the menus of VS Code itself.

In the OM Core side panel, press Start Runtime and wait until the Runtime row shows Running (a few seconds). Then press Open GUI: the OM Core tab opens and the GUI row shows Connected.
In the File menu at the top of the OM Core tab, choose Open… and pick examples/DEMO-03--CALC-FLOW-20260623-0057-5Y-ONLY.json inside the om-core folder.
In the Model Browser on the left of the tab, open Views → Drivers. These are the assumptions by year: prices, volumes, cost percentages and so on. PriceGadgets is 120 in every year.
Open Views → PnL. For 2028, RevenueGadgets is 624000 and NetIncome is 158112.
Go back to Drivers, double-click PriceGadgets for 2028, type 130, press Enter. In PnL, 2028 RevenueGadgets becomes 676000 and NetIncome becomes 164851.2. The other years do not change, because each year has its own price.
Ctrl+Z undoes the change, Ctrl+Y (or Ctrl+Shift+Z) redoes it.
Select a cell, for example NetIncome in PnL, and open the Calculation Flow tab in the bottom panel of the tab to see which cells it is calculated from.
File → Save… (the tab's menu) saves the model as a .json file. File → Open… loads it again.

The other files in examples open the same way. Some of them use features this preview does not support yet, for example formatting.

When you are done, press Stop Runtime in the side panel. Closing VS Code also stops the engine that the extension started. Either way, changes that were not saved with File → Save… are lost.

The OM Core side panel

The rows at the top show the state; hover over a row for details. Some rows have a button that appears when you hover over the row (for example Start or Stop on Runtime, Open GUI or Reconnect on GUI, Manage Workspace Trust in Restricted Mode); the same actions, and more (choose or show the om-core folder), are in the row's right-click menu. The panel header has a refresh button and, in its … menu, Reconnect.

Below the rows, the Actions section has:

Start Runtime, which becomes Stop Runtime while the engine OM Tools started is running.
Open GUI, which becomes Close GUI while the tab is open.
Settings, which opens the OM Core settings.

The runtime and GUI buttons are independent. Open GUI only opens the tab and connects it to an engine that is running; it never starts one, and without an engine the tab says disconnected and what to do. Closing the GUI does not stop the engine. Stopping the engine does not close the tab: it shows disconnected and connects by itself when you press Start Runtime again, with a new, empty model. An engine that was started outside OM Tools (a terminal, the om-core Qt GUI) has no Stop button: OM Tools cannot stop it.

Commands

All of these are in the command palette (Ctrl+Shift+P).

Command	What it does
`OM Core: Start Runtime`	Starts the engine: `uv` runs om-core from `omCore.omCorePath`. Does not open the GUI; a GUI tab that is already open connects to it.
`OM Core: Stop Runtime`	Stops the engine that the extension started, with everything it started. The model in it is lost unless it was saved.
`OM Core: Open GUI`	Opens the grid GUI in an editor tab and connects it to a running engine. Does not start the engine.
`OM Core: Close GUI`	Closes the GUI tab. The engine keeps running and keeps the model.
`OM Core: Reconnect to Runtime`	Reconnects the GUI to a running engine if it shows `disconnected`.
`OM Core: Refresh Status`	Re-checks the state shown in the side panel (it also updates by itself).
`OM Core: Choose om-core Folder…`	Picks the om-core folder and saves it to `omCore.omCorePath` in User settings.
`OM Core: Open Settings`	Opens the OM Core settings.
`OM Core: Reveal om-core Folder in File Explorer`	Shows the om-core folder in your file manager.

Settings

Setting	Default	Meaning
`omCore.omCorePath`	empty	Folder of the om-core clone (the one with `main.py`). Required by Start Runtime; when empty, it asks for the folder once.
`omCore.runtimeEndpoint`	empty	Address of the engine, e.g. `tcp://127.0.0.1:17391`. Empty means the default: local TCP port 17391 on Windows, the socket `/tmp/openm-<user>.sock` on macOS and Linux.
`omCore.showSystemElements`	`false`	Show system elements (names starting with `%`) in the Model Browser, tabs and selectors.

Not available in this preview

These items are visible but disabled, with the hint "Not available in this preview version":

Edit: Paste as New Cube, Convert Selection to Dimension Labels, Assign Item Labels from Selection, Delete Selected Dimension Items
Model: Add Group to Row/Col Dim; Add Group, Move Selection To Group, Ungroup, Add Aggregate Item in the grid context menu
View: Format Toolbox, Performance Watch, Timeline
Tools: Calculation Engine, Options
Window: New Window, Close Window
Formatting buttons in the toolbar (Bold, Italic, Underline, Fill, Font, Format)
Circular References tab in the bottom panel

Known limitations

Changes to rules and to the dimensions placed on the grid axes cannot be undone with Ctrl+Z. Ctrl+Z after such a change reverts the previous value edit instead. This comes from the engine, not from the extension.
Number formats are not applied in the grid yet.
The engine starts with a small placeholder model; File → Open… in the OM Core tab replaces it.
.openm script files cannot be opened from File → Open… in the OM Core tab. It reads .json models only. Run .openm scripts with the om-core command line (uv run python main.py --batch file.openm).

Troubleshooting

Engine path: "Not set". Press Settings in the side panel and click Choose folder… (step 4), or just press Start Runtime: it asks for the folder. Canceling that dialog gives "om-core path is not set".

"omCore.omCorePath does not exist: … — trying auto-detect". The folder in the setting is gone or mistyped. OM Tools then asks for the folder; choose the om-core clone.

Engine path: "… — not an om-core folder". The setting points to a folder without main.py (for example the parent folder). Choose the om-core folder itself.

Dependencies: ".venv missing — run uv sync". Run uv sync in the om-core folder (step 2), then press Start Runtime.

uv: "Not found" or "Not on PATH — restart VS Code". Install uv (step 1). If it is installed, close all VS Code windows and start VS Code again.

"This workspace is not trusted (Restricted Mode)…". You opened a folder that VS Code does not trust, and OM Tools does not run code from there. Press Manage Workspace Trust on the Runtime row and trust the folder, or open VS Code without a folder.

"Failed to start runtime: …". The message ends with the engine's error output. The usual causes are the ones above: uv is not found, uv sync was not run, or the folder is not om-core.

The GUI shows "disconnected". If the engine is not running, press Start Runtime in the side panel: the tab connects by itself. If it is running, press Reconnect on the GUI row (or run OM Core: Reconnect to Runtime).

Another engine is already running. If an engine is already running at the same address (on Windows, port 17391), for example the om-core Qt GUI or an earlier run, Open GUI connects to it and you see that engine's model, and Start Runtime does not start a second one. Stop that process where it was started: Stop Runtime only stops an engine that OM Tools started itself.

Development

npm install
npm run build
npm run compile
npm test

npm test talks to a running OM Core runtime and changes the model in it: use a throwaway runtime, not one with your own model.

The runtime configuration and integration notes are in AGENTS.md. To use the extension, a compatible OM Core runtime is required.

Community and governance

License

OM Tools is distributed under the GNU Affero General Public License, version 3 or later (AGPL-3.0-or-later), as declared in package.json, except for separately licensed materials. See LICENSE, NOTICE, and third-party notices.

OM Core is a separate repository with its own contributor policies and notices; signing an OM Tools agreement does not automatically sign an agreement for OM Core.

OM Core

Cloudcell