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Installation

Follow these steps to install the X21 Excel add-in on a Windows workstation. The add-in ships as a ClickOnce application signed with your team’s certificate and bundles the Deno backend, React task pane, and VSTO components.

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Prerequisites

Usually all those are installed by default on modern Windows systems:
  • Windows 10 (build 19045+) or Windows 11 with Excel 2016 or later (desktop edition).
  • .NET Framework 4.8 – required by the VSTO runtime.
  • WebView2 Runtime (usually installed with Microsoft Edge). If missing, download from Microsoft.
  • Required ports available on localhost: 8000+ for the Deno API, 8085+ for WebSockets, and 8080+ for the Excel API bridge. The add-in automatically finds a free port close to these defaults and writes it to %LOCALAPPDATA%\X21\deno-*.

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Choosing an Installation Channel

X21 publishes multiple ClickOnce channels through the Publish.ps1 script:

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Installing via ClickOnce

  1. Navigate to the ClickOnce URL for your target channel or run the generated setup.exe from the publish directory.
  2. Click Install. The bootstrapper installs the VSTO add-in, registers necessary registry keys, and places the backend binaries under %LOCALAPPDATA%\X21.
  3. Launch Excel. If it’s already running close all Windows also via task manager or restarting your PC.
  4. Look for the X21 ribbon tab. Open the task pane using the AI Chat button or Ctrl+Shift+A