No such thing. If you want cheap flights you have to do your homework.

I should point out that Google Flights does not work world-wide. It may work for US-originating flights, but it's not universal.

ITA is good but you can't book anything there, so then you have to really try to get the fares you want on other sites. I recently purchased 2 TATL tickets, an AF/KL itin. DL.com, AF.com and KL.com all offered different options, all more expensive than what I had found on ITA. I ended up buying the tickets I wanted for a significantly lower price (the ITA price) at Expedia. These were AF/KL flights, DL stock, DL-coded - yet they were far more expensive at DL.com.