@mindstone-engineering/mcp-server-office

@mindstone-engineering/mcp-server-office

Microsoft Office MCP server — read and edit Word documents, Excel workbooks, and PowerPoint presentations from a Model Context Protocol host.

This package bundles three pieces that version together:

• Stdio MCP server (dist/index.js) — exposes ~50 Office tools over MCP
• Office sidecar (dist/sidecar/cli.js) — a local HTTPS server that bridges the MCP process and the Office task pane over WebSocket
• Office Add-in assets (dist/addin/, manifest.xml) — the task pane HTML/JS sideloaded into Word, Excel, and PowerPoint

Desktop-only: Office Add-in sideload and office-addin-dev-certs HTTPS cert generation only work on desktop operating systems (macOS, Windows). There is no cloud mode.

Requirements

• Node.js 20+
• npm
• macOS or Windows with Microsoft 365 Word, Excel, and/or PowerPoint installed
• First-run admin prompt on Windows to trust the dev certificate (one-time)

Quick Start

Install & build

cd <path-to-repo>/connectors/office
npm install
npm run build

npx (once published)

npx -y @mindstone-engineering/mcp-server-office

Local

node dist/index.js

How it works

• The host (e.g. Mindstone Rebel) spawns the stdio MCP server.
• The MCP server expects a running Office sidecar — it discovers it via the state file path in REBEL_OFFICE_SIDECAR_STATE.
• If no sidecar is running, the MCP server lazy-spawns one from dist/sidecar/cli.js.
• On first start, the sidecar generates a trusted localhost HTTPS certificate (office-addin-dev-certs), binds to port 52100 (with a small fallback window), writes manifest.word.xml / manifest.excel.xml / manifest.powerpoint.xml into each Office app's WEF folder, and writes a state file containing its port + auth token.
• Office detects the sideloaded manifests at launch and shows a Rebel ribbon button. Clicking it opens the add-in task pane, which connects back to the sidecar over authenticated WebSocket.
• Tool calls on the MCP server are forwarded via HTTPS to the sidecar, then routed over WebSocket to the task pane, which calls the Office.js APIs in the Word/Excel/PowerPoint context.

Configuration

Environment variables

Read by the stdio MCP server (dist/index.js):

• REBEL_OFFICE_SIDECAR_STATE — required. Absolute path to the sidecar state file (JSON). The MCP server reads port and token from this file to talk to the sidecar; the sidecar writes it on startup. The state file's parent directory doubles as the sidecar's state directory (certs, per-app manifests).
• REBEL_DISABLE_OFFICE_SIDECAR — optional kill-switch. When set (1), the MCP server refuses to talk to or spawn the sidecar.

Read by the sidecar (dist/sidecar/cli.js) — normally set by the MCP server when it lazy-spawns the sidecar, but documented here for hosts that manage the sidecar lifecycle directly:

• REBEL_OFFICE_SIDECAR_STATE_DIR — required by the sidecar. Directory for the state file, HTTPS certificates, and generated per-app manifests (manifest.word.xml, manifest.excel.xml, manifest.powerpoint.xml). The MCP server derives this from the parent directory of REBEL_OFFICE_SIDECAR_STATE and passes it through automatically.
• REBEL_OFFICE_ADDIN_DIR — optional. Absolute path to the built add-in static files (the directory containing taskpane.html, taskpane.js, and assets/). The MCP server sets this to the package's dist/addin/ directory; hosts serving a custom add-in bundle can override it.

Host configuration examples

Claude Desktop / Cursor

The Office connector is designed to be managed by a host application (like Mindstone Rebel) that owns the sidecar lifecycle. Running it directly from Claude Desktop is possible but the host must provide a writable REBEL_OFFICE_SIDECAR_STATE path.

{
  "mcpServers": {
    "Office": {
      "command": "npx",
      "args": ["-y", "@mindstone-engineering/mcp-server-office"],
      "env": {
        "REBEL_OFFICE_SIDECAR_STATE": "/absolute/path/to/sidecar-state.json"
      }
    }
  }
}

Mindstone Rebel

"RebelOffice": {
  "name": "RebelOffice",
  "type": "stdio",
  "command": "npx",
  "args": ["-y", "@mindstone-engineering/mcp-server-office@0.1.0"],
  "env": {
    "REBEL_OFFICE_SIDECAR_STATE": "~/Library/Application Support/mindstone-rebel/office-sidecar/sidecar-state.json"
  },
  "description": "Microsoft Office integration — Word, Excel, PowerPoint.",
  "catalogId": "bundled-office"
}

Tools (~50)

• Setup: rebel_office_setup, rebel_office_status
• Word (17): document read/write, selection, search-replace, track-changes, styles, list manipulation, image insert, comments, etc.
• Excel (22): workbook/sheet/range read-write, formulas, formatting, named ranges, tables, charts, pivots, filters, validation, etc.
• PowerPoint (12): slide manipulation, text/shape/image insert, master/layout reads, notes, export, etc.

The authoritative tool list and schemas are registered in src/index.ts and returned by listTools.

Smoke test

REBEL_OFFICE_SIDECAR_STATE=/tmp/rebel-office-smoke/sidecar-state.json \
  node dist/index.js

Then send a listTools MCP request on stdin; you should get back the full tool manifest. The server does not need a live sidecar to respond to listTools.

Licence

FSL-1.1-MIT — Functional Source License, Version 1.1, with MIT future licence. The software converts to MIT licence on 2030-04-08.

Security

See SECURITY.md for this connector's security policy and the repository-level SECURITY.md for vulnerability reporting.

Known drift risk: vendored code from the Mindstone Rebel monorepo

Some files in this package are byte-compatible copies of code that also lives in the Mindstone Rebel monorepo (github.com/mindstone/MindstoneRebel). They have to stay in sync on both sides; there is no automation today.

Vendored from Rebel's src/shared/sidecar/ (wire-format contract between Rebel's main process and this sidecar CLI):

• src/shared/sidecar/stateFile.ts
• src/shared/sidecar/readySignal.ts
• src/shared/sidecar/constantTime.ts
• src/shared/sidecar/errorMessages.ts

Vendored from Rebel's src/core/appBridge/ (minimum slice needed for the sidecar bundle; ~1,444 LOC across four files):

• src/shared/appBridge/server/commandRouter.ts
• src/shared/appBridge/server/connectionManager.ts
• src/shared/appBridge/shared/errors.ts
• src/shared/appBridge/shared/protocol.ts

If the Rebel-side files change, this package's copies will drift silently. The state-file / ready-signal schemas in particular are a wire-format contract — the Rebel main process parses what the sidecar writes — and a silent drift will surface as runtime ReadySignalSchema.safeParse() failures or sidecar startup regressions.

TODO — future work

Extract these into their own published package (e.g. @mindstone-engineering/app-bridge-core plus a shared sidecar-protocol package) so they become versioned contracts rather than vendored code.

Until then: anyone touching either side must manually keep both copies in sync. When editing here, diff against the corresponding file in the Rebel monorepo (src/shared/sidecar/* and src/core/appBridge/*) and copy the change across before landing. Both sides are covered by their own test suites but neither proves the other's copy is byte-current.