I've built my service https://urlscan.io to some extent to be able to track the impact of certain scripts / hosts on the overall size of the website. You can find the breakdown by hostname under "Request Stats" on the right. But, for this use case, it would be perfectly sufficient to use the Chrome Devtools and filter by "facebook" for example. Here is a scan where the 200KB Facebook sdk.js is being transferred (62KB…
Facebook's like button code generator tool[1] includes the entire SDK even if you configure it to only show a like button with no other social graph features. I guess there is an argument that having every site that uses Facebook's API having the same .js file will take advantage of browser caching better but it's still irritatingly wasteful. [1] https://developers.facebook.com/docs/plugins/like-button
1/ is better (proper resizing in different locales) but 2/ is always an option and it saves 60K of JS