Purpose:
Deep Search 99 searches the other 99% of the internet, excluding most of the big brands that tend to clutter the results.
It also tries to exclude "popular" sites that tend to cause more harm than good, due to bad information or disrespecting the people their site is about. You can view the entire block list here, along with more information.
It might also "boost" certain sites that are particularly helpful that may not otherwise get enough recognition. This is just basically to make up for Google's way of ranking sites by domain "authority" rather than usefulness.
Sub-topic Search Engines:
I will make more custom search engines for certain sub-topics that I search about often as well, in cases where too many of the best-ranking results tend to have the same shallow generic information.
Sometimes Google's Custom Search makes some API errors for no apparent reason. I want to drop Google eventually, but finding decent alternatives is difficult.
If you're getting API errors, it may be because of your ad/script blocker. For uBlock Origin, adding these lines in the My Filters box should fix it:
@@||www.googleapis.com/generate_204 @@||clients1.google.com/generate_204
Sub-topics:
Natural Health Search | Code Search | Inline Skating Search