Buzzkill
I am not sure that there is much difference as you have to put the url of the website in first and if you go to the top website for any given keyword and put that url it will return the keywords and surely they are not at the top of the organic listings for using the wrong keywords.
What?
Detecting search keywords for which a site is ranked high.
With online free seo tool Seodigger.com you can find out for which keywords your site ranks high enough to be in Google Top 20. You can analyze your own sites as well as sites of your competition, using the information obtained for SEO analysis, building a semantic core, finding out how well is a site optimized for this or that search request, and a lot more. Apart from a list of search queries, wordtracker and overture results are also determined (keyword popularity calculated by Wordtracker.com and Overture.com). Data is CSV-exportable.
How exact?
Request database contains 60 million popular keyphrases, first 20 requests are processed.
Keyword and keyphrase database contains 60 million popular search queries. First 20 SERP positions are processed per every request. Free seo service accomplish complete update every 2 weeks.
For whom?
For webmasters and SEO professionals.
Registered users can get information per entire domain as well as per separate pages. This increases the number of data analysis options dramatically. There is no limit concerning maximum number of keywords per pages, and there can be up to 10 requests per hour for the entire domain. For every registered user, request history is saved. Those who did not register can check up to 5 requests per hour, and only results for separate pages are available.
But if you want to be absolutely sure of ripping the keywords that a website is using them just use keyword swipe which you can easliy get hold of in the forum.
Again you have to put the url into keyword swipe and it will return keywords for that url when its finished click in the bottom right hand corner and extract them it wil put them into notebook in text form ready for you to use.
Here is a little tip for using keyword swipe that it is not sold for but l use it for, if you put the url in thats the main index page it will return every single page listed in that website and l mean every single page, you can find the most interesting pages when your trying to find out how certain pages are written......like downloads etc
nicho