Technology we use
This tool attempts to simulate what happens when a user visits a specified page with a typical browser, without clicking on anything. The browser has no addons/extensions installed, and Do Not Track (DNT) is not enabled, since this is the default setting in most browsers.
We built the tool with Phoenix Framework and Puppeteer (we previously used PhearJS+PhantomJS instead of Puppeteer).
We don't provide an API as we have limited resources and PhantomJS is rather resource-intensive, but the code is available under the MIT license.
Please note, however, that this tool is mainly meant to be used as a starting point for web developers. For more rigorous and systematic testing we recommend that you check out OpenWPM, which we used to analyze the websites of Sweden's municipalities (site, code). You might also want to have a look at PrivacyScore, which is a bit more comprehensive than Webbkoll (additionally checks e.g. email and TLS/SSL configuration) and also lets you compare/rank lists of sites.