how to make a metadata-search engine?

hi everyone
I was searching for weeks on how to make a metadata-search engine but no luck!
if anyone has an idea how or what script are they using please tell me!
example- getcouponhere.com

thank you!

I dont really understand the question, do you mean to crawl/scrape data from coupon sites, store them, and create an API for users to search them?
Or you mean to use an existing search engine API, and enter a keyword parameter for example "meta:cbd oil" ?