They could open source everything else. I'm pretty sure they don't do their own ranking anyway.

You can make the ranking configurable. Once we get our own index built we will go back to doing this. The way we used to do it was by having a PostgreSQL function that is customizable once you get everything set up...I'm sure there are other ways to do it as well.

No, they get their search results (and rankings) from Bing and Yandex so it wouldn't matter.

just open a guest window from chrome, and type the same search terms in the two different search engines, and you would see different results. it's not hard to verify.

What are you saying? That DDG is not getting their search results from Bing and Yandex?

From your source:

In fact, DuckDuck Go gets its results from over four hundred sources. These include hundreds of vertical sources delivering niche Instant Answers, DuckDuckBot (our crawler) and crowd-sourced sites (like Wikipedia, stored in our answer indexes). We also of course have more traditional links in the search results, which we also source from a variety of partners, including Oath (formerly Yahoo) and Bing.

We continue to partner with more and more sources to bring you the best Instant Answers from the best sources. Our focus is on synthesizing it all together into a superior search experience.

I suppose that's quite different than 'DDG is a frontend to Bing results'?

It depends. For me, a search engine is about the organic search results and they get all their organic search results from Bing, Oath and Yandex. The 400 sources they talk about are used for Instant Answers, boxes and stuff like that.

Essentially it's Bing for the web results. The other 399 sources seem to be for non web things.

Source?

Not available. DDG is closed source.

Really... You read the last part of that paragraph, but no the first?

>In fact, DuckDuckGo gets its results from over four hundred sources. These include hundreds of vertical sources delivering niche Instant Answers, DuckDuckBot (our crawler) and crowd-sourced sites (like Wikipedia, stored in our answer indexes).

Kinda silly to have a crawler that doesn't index anything.

They have an index but just for their Instant Answers (for which they have 400 sources) and not the organic search results. The last paragraph is what's relevant to the actual search index.

Easy way to verify this, right-click on the ads, paste link