By default the local dev server (ran using npm run amo) will load data from the local docker instance (usually found at http://olympia.test/). Admittedly this dataset is incomplete and small. While we discourage usage of the production API for development, you can safely develop against the “Dev” or “Stage” servers using npm run amo:dev or npm run amo:stage. This will give you a large amount of data to work with when testing out new features.
It’s best to use these commands rather than setting the API_HOST and other environment variables directly: these commands automatically set the API and CDN variables appropriately so screenshots, icons, etc. will load correctly.