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arXiv
2.4M+ free preprints in physics, math, CS and more — uploaded by the authors themselves, fully legal, and often available months before journal publication.
Why the legal distinction matters
Lists that open with shadow libraries treat "free" as one category. It isn't:
- Open access — the author or publisher chose to make it free (arXiv, PLOS, DOAJ journals). Stable, safe, citable.
- Public domain — copyright expired (Project Gutenberg's 70,000+ books). Free forever, everywhere.
- Shadow libraries — copyrighted work shared without permission. Legality varies by country, domains vanish constantly, and the ecosystem of fake mirror sites is a top malware vector.
Practical risk: when a famous shadow site's domain gets seized, dozens of lookalike clones appear — and some serve credential-stealing scripts. If you can't verify the domain, don't log in or download executables. The legal routes below solve most needs anyway.
The legal route to almost any paper
- Google Scholar — click "All N versions"; a free author copy often hides there.
- Unpaywall / OA Button — browser extensions that auto-find legal open-access copies. Unpaywall finds one for roughly half of recent papers.
- Preprint servers — arXiv, bioRxiv, SSRN: the author's own manuscript, free.
- Email the author — researchers may share their own PDFs on request, and most are happy to.
- Your library — public and university libraries license enormous databases; interlibrary loan fills the gaps.
That five-step ladder legally resolves the vast majority of "paywalled paper" problems.
Spot a risky "free" site in 10 seconds
- Domain roulette: the site tells you to "use our new domain" every few months — a hallmark of takedown evasion.
- Download buttons that multiply: more than one "Download" button usually means ads dressed as downloads.
- Asks for login to a service it doesn't own — never enter institutional credentials on third-party sites.
- Executables for documents: a PDF should never arrive as an .exe or ask you to install a "codec."
- No about page, no operators, no takedown policy: legitimate archives (Internet Archive, Gutenberg, DOAJ) tell you exactly who runs them.