Tool for obtaining a BibTeX entry from a key, without creating it manually I am looking for a tool, where I only need to write something like alessandroni2015bibtex (this very question) to obtain the BibTeX entry, without needing to rewrite it.

I am aware that Google Scholar always offers a BibTeX link and uses AuthorYearFirst_Word as a scheme, but I do not know how to use this key for searching, because Google uses an internal ID for each BibTeX. Thus, when I feed the data of my citation to Google Scholar, sometimes I do not find it. For example, in case of books, I find only new editions (maybe due to a wrong use of the tool).
I doubt it. In all but the most verbose or non-human friendly (e.g., DOI) key style, the problem is a one-to-many mapping in that each BibTeX key maps to many sources even though any single source has just a single BibTex key. Even in relatively small personal bib files, conflicting keys are common and need to be disambiguated (usually with an additional letter or number).  The bigger the database (and Goggle Scholar is a big database) means that there will be lots of collisions.