ext-apps/examples/scenario-modeler-server/README.md
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# 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://modelcontextprotocol.github.io/ext-apps/screenshots/scenario-modeler-server/01-compare-to.png"><img src="https://modelcontextprotocol.github.io/ext-apps/screenshots/scenario-modeler-server/01-compare-to.png" alt="Compare to" width="100%"></a></td>
<td><a href="https://modelcontextprotocol.github.io/ext-apps/screenshots/scenario-modeler-server/02-bootstrapped-growth.png"><img src="https://modelcontextprotocol.github.io/ext-apps/screenshots/scenario-modeler-server/02-bootstrapped-growth.png" alt="Bootstrapped growth" width="100%"></a></td>
<td><a href="https://modelcontextprotocol.github.io/ext-apps/screenshots/scenario-modeler-server/03-vc-rocketship.png"><img src="https://modelcontextprotocol.github.io/ext-apps/screenshots/scenario-modeler-server/03-vc-rocketship.png" alt="VC rocketship" width="100%"></a></td>
</tr>
</table>
## 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 start
```
The server will listen on `http://localhost:3001/mcp`.
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[RESOURCE_URI_META_KEY]`.
### 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