manifest.json serves as the 'manual' for the extension package, defining the extension's metadata, server configuration and permission requirements. The file uses a declarative syntax that allows developers to specify basic information such as extension name/version, and more importantly, user inputs (e.g. API Key) and how they are securely stored. When Claude Desktop starts the server, it will automatically inject the configuration parameters through the environment variable ${user_config.api_key}. This design not only ensures that sensitive data is stored through the operating system key chain, but also automates the configuration process.
This answer comes from the articleAnthropic's New Game: Can Desktop Extensions Break Down the Installation Barriers for Native AI?The
