🔍 Unpaywall DOI Finder

Enter a paper's DOI and instantly check whether a free, legal open-access version exists — via Unpaywall's database of 50+ million papers. No API key or account required.

Digital Object Identifier (DOI)

⏳ Looking up DOI via Unpaywall…

Result

💡 Unpaywall is a non-profit database of legal open-access versions. If a paper is not found, it may not have an open-access version yet — check the journal's own website or contact the authors directly for a preprint.

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📎 BibTeX Checker 📚 Citation Formatter

Finding open-access versions of research papers

The Unpaywall database indexes legal open-access versions of over 50 million research papers — preprints, author accepted manuscripts in institutional repositories, and gold open-access publications. This tool queries Unpaywall directly using a paper's DOI (Digital Object Identifier) and reports whether a free legal version exists and where.

Types of open-access versions

Publisher (gold OA): the final published version, free on the publisher's website. Hybrid: a subscription journal where the specific article was published open access (often via APC payment). Green OA: an author accepted manuscript or preprint deposited in a repository (PubMed Central, institutional repository, arXiv, bioRxiv). Version of record: the final typeset version. These have different citation implications — cite the version of record, not the preprint, wherever possible.

When Unpaywall finds nothing

Not finding an OA version in Unpaywall does not mean none exists — it may not yet be indexed. Try searching the author's institutional repository directly, PubMed Central, or Google Scholar. Many authors share their papers on request — the "Email PDF" button on ResearchGate exists for this purpose. Some journals have embargo periods before OA versions are released (typically 6–12 months).