What is claude-plugin-m365-gateway?

Claude for Microsoft 365 is an official add-in that brings AI assistance directly into Word, Excel, PowerPoint, and Outlook. By default it routes requests through Anthropic's own servers. This project, claude-plugin-m365-gateway, is a self-hosted bridge that intercepts those requests and redirects them to any compatible AI provider you choose instead, whether that is a local model running on your own hardware, a third-party API service, or Anthropic's API directly. The bridge is built from two pieces running together. Caddy is a web server that handles encrypted HTTPS connections and the security headers the Office add-in requires. LiteLLM sits behind Caddy and acts as a translator: the Office add-in speaks Anthropic's message format, but LiteLLM converts that into whatever format your chosen AI provider expects, then converts the response back. The result is that the Office add-in works without changes while your requests go to the backend you configured. To set it up you need a server, a domain name pointing to that server, and a compatible AI provider. You edit a few configuration files to specify your provider's address and API key, then launch the whole stack with a single Docker command. Docker is a tool that packages software so it runs consistently anywhere. Caddy automatically obtains a security certificate so traffic is encrypted. Once running, you open the Claude add-in inside any Office application, choose the enterprise gateway option on the sign-in screen, and enter your gateway's address. The full README was longer than what was shown, so some configuration details may not appear here.