# Example: SaaS Scenario Modeler

A React-based demo MCP App that lets users adjust SaaS business parameters and see real-time 12-month projections of revenue, costs, and profitability with comparison against pre-built scenario templates.

<table>
  <tr>
    <td><a href="https://apps.extensions.modelcontextprotocol.io/screenshots/scenario-modeler-server/01-compare-to.png"><img src="https://apps.extensions.modelcontextprotocol.io/screenshots/scenario-modeler-server/01-compare-to.png" alt="Compare to" width="100%"></a></td>
    <td><a href="https://apps.extensions.modelcontextprotocol.io/screenshots/scenario-modeler-server/02-bootstrapped-growth.png"><img src="https://apps.extensions.modelcontextprotocol.io/screenshots/scenario-modeler-server/02-bootstrapped-growth.png" alt="Bootstrapped growth" width="100%"></a></td>
    <td><a href="https://apps.extensions.modelcontextprotocol.io/screenshots/scenario-modeler-server/03-vc-rocketship.png"><img src="https://apps.extensions.modelcontextprotocol.io/screenshots/scenario-modeler-server/03-vc-rocketship.png" alt="VC rocketship" width="100%"></a></td>
  </tr>
</table>

## MCP Client Configuration

Add to your MCP client configuration (stdio transport):

```json
{
  "mcpServers": {
    "scenario-modeler": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-scenario-modeler",
        "--stdio"
      ]
    }
  }
}
```

### Local Development

To test local modifications, use this configuration (replace `~/code/ext-apps` with your clone path):

```json
{
  "mcpServers": {
    "scenario-modeler": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/scenario-modeler-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    }
  }
}
```

## Features

- **Interactive Parameters**: 5 sliders for Starting MRR, Growth Rate, Churn Rate, Gross Margin, and Fixed Costs
- **12-Month Projections**: Line chart showing MRR, Gross Profit, and Net Profit over time
- **Scenario Templates**: 5 pre-built business strategies (Bootstrapped, VC Rocketship, Cash Cow, Turnaround, Efficient Growth)
- **Template Comparison**: Overlay dashed lines to compare your scenario against any template
- **Summary Metrics**: Key metrics including Ending MRR, Total Revenue, Total Profit, and break-even month
- **Theme Support**: Adapts to light/dark mode preferences

## Running

1. Install dependencies:

   ```bash
   npm install
   ```

2. Build and start the server:

   ```bash
   npm run start:http  # for Streamable HTTP transport
   # OR
   npm run start:stdio  # for stdio transport
   ```

3. View using the [`basic-host`](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-host) example or another MCP Apps-compatible host.

## Architecture

### Server (`server.ts`)

Exposes a single `get-scenario-data` tool that returns:

- 5 pre-built scenario templates with parameters, projections, and summaries
- Default input values for the sliders
- Optionally computes custom projections when `customInputs` are provided

The tool is linked to a UI resource via `_meta.ui.resourceUri`.

### App (`src/`)

- Built with React for reactive slider updates and derived state management
- Uses Chart.js for the line chart visualization
- All projection calculations run client-side for instant slider feedback
- Components: `SliderRow`, `MetricCard`, `ProjectionChart`
- Template comparison shown as dashed overlay lines on the chart