Spreadsheet MCP App

A streaming spreadsheet MCP App built with Skybridge. Claude renders interactive spreadsheets in real-time — cells appear with animations as the model streams its response.

Features:

• Streaming — cells render progressively as the model types
• Sparse addressing — only populated cells are sent, gaps are automatic
• Auto-sizing columns — widths adjust to content
• Resizable columns — drag column borders to resize
• Fullscreen mode — expand to fill the viewport with sticky headers and infinite scroll
• Dark mode — respects system theme
• Links — URLs and emails are auto-detected and clickable

Prerequisites

Node.js (v22+)

• macOS: brew install node
• Linux / other: nodejs.org/en/download

cloudflared (for tunneling to Claude)

• macOS: brew install cloudflared
• Linux / other: developers.cloudflare.com/cloudflare-one/connections/connect-networks/downloads

Setup

1. Install dependencies

npm install

2. Start the dev server

npm run dev

The server runs at http://localhost:3000. Skybridge DevTools are available at http://localhost:3000 for local testing without Claude.

Connecting to Claude

Tunnel your local server with cloudflared to get a public URL:

cloudflared tunnel --url http://localhost:3000

Then add your tunnel URL with /mcp appended (e.g. https://xxx.trycloudflare.com/mcp) as a remote MCP server in Claude settings.

Tool: spreadsheet

The server exposes a single tool that Claude uses to render spreadsheets.

Input format: CSV string with columns cell,value,style — one row per cell.

Column	Description	Example
cell	Excel-style address	A1, B2, C10
value	Text or number	Revenue, $50000
style	Optional inline CSS	font-weight: bold

Example input:

A1,Revenue,font-weight: bold
B1,Q1,font-weight: bold
C1,Q2,font-weight: bold
A2,Sales,
B2,$120000,
C2,$145000,
A3,Costs,
B3,$80000,
C3,$92000,

Try it: Ask Claude something like "Make a spreadsheet comparing Q1-Q4 revenue for 3 product lines".

Project Structure

spreadsheet-mcp-app-skybridge/
├── server/src/
│   ├── index.ts          # Express app with static serving & MCP middleware
│   ├── server.ts         # McpServer with tool/widget registration
│   └── middleware.ts     # Streamable HTTP transport middleware
├── web/src/
│   ├── helpers.ts        # Typed Skybridge hooks (useToolInfo)
│   ├── index.css         # Spreadsheet styles, dark mode, sticky headers
│   └── widgets/
│       └── spreadsheet.tsx  # React grid component
├── web/vite.config.ts
├── tsconfig.json
└── package.json

Production Build

npm run build
NODE_ENV=production node dist/server/src/index.js

Built With

• Skybridge — full-stack framework for MCP Apps
• MCP Apps (ext-apps) — open standard for interactive UI in MCP