I use Google Search.

You can write your own scraper (if you're very smart), or purchase one off the shelf.

Every website application will have its own algorithm tweak, so its hard to really trust just one. SimilarWeb's problem is that it pulls information from various other APIs and so the return is often wrong. I once launched that I knew had little traffic yield a result of almost 6k per month. What you should do is use a combination of apps along with the easiest one to measure - Google Incognito - by clearing your cache and using this browser you can search as a 'random' and get pretty good results. Unless you put a location Google Incognito tends to give global results based on keyword matching (as long as is not a local business) compare the results with apps like Similar Web, Hubspots, Neil Patel's, SpyFu, etc.