The extension.json file contains the manifest for an Extension and needs to be placed in a public directory. You are required to provide a manifest file to publish an Extension to the Extensions Store.
The data API allows you to get information and metadata exposed from Replit's GraphQL API.
The fs or filesystem API allows you to create, read, and modify files on the repl's filesystem.
The init() method initializes the Extension, establishes a handshake with the Repl, and adds an event listener to the window object. It takes as an argument an object containing optional parameters for the initialization process. It returns a function that removes the event listener added to the window object.
The messages API allows you to send custom notices in the Replit workspace.
ReplDB is a simple key-value store available on all repls by default. Extensions can use ReplDB to store repl specific data.