Hit a paywall? Paste a DOI or title, one per line, and this looks for a legal free copy: an open-access version, an author manuscript in a repository, a preprint, or a PubMed Central copy.
This searches open-access records and repositories. It never links to pirated copies, so nothing from sites like Sci-Hub appears here.
Not every paper has a free version, so misses are normal. When there is no free copy, the fastest route is often to email the author, who is usually glad to share it.
Runs in your browser against OpenAlex and Unpaywall, both free. Nothing is stored.