ext-apps/examples/scenario-modeler-server

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.

MCP Client Configuration

Add to your MCP client configuration (stdio transport):

{
  "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):

{
  "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:

   npm install
   

2. Build and start the server:

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

3. View using the 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