How to Use Unpaywall to Find Free PDFs and Convert to EPUB
Unpaywall is one of the most useful tools for academic researchers — it finds free legal versions of paywalled papers automatically. Once you have the PDF, converting to EPUB gives you a far more comfortable reading experience on any e-reader or phone.
What is Unpaywall?
Unpaywall (unpaywall.org) is a free browser extension that scans its database of 50+ million open-access papers whenever you visit a publisher paywall page. If a free legal version exists anywhere — PubMed Central, arXiv, an institutional repository, a publisher's own open-access archive — Unpaywall shows a green tab on the right edge of your browser and links you to the free PDF directly.
It's used by millions of researchers and is integrated into many library and reference management tools.
Installing Unpaywall
- Go to unpaywall.org
- Click Get the extension → installs in Chrome or Firefox in seconds
- No account or login required — it works immediately after installation
Finding free papers with Unpaywall
- Visit any academic paper page — from a journal publisher, PubMed, Google Scholar, etc.
- Look for the green tab on the right edge of the browser window
- If it appears, click it — the free PDF opens directly
- If the tab is grey, no free version was found (see alternatives below)
You can also use the Unpaywall data API to check any DOI programmatically: https://api.unpaywall.org/v2/[DOI]?email=[your@email.com]
Converting the PDF to EPUB
- Download the PDF via the Unpaywall green tab
- Go to pdf2epub.toolkit.bot
- Upload the PDF
- Wait ~30 seconds
- Download the EPUB
Transfer to your e-reader: email to Kindle, USB to Kobo, or open in any EPUB app. The EPUB has reflowable text, adjustable font size, and chapter navigation — far more readable than the PDF on a phone or e-reader screen.
When Unpaywall can't find a paper
If the Unpaywall tab is grey, try these in order:
- Semantic Scholar: Search the title at semanticscholar.org — often finds PDF links Unpaywall misses
- ResearchGate: Search the title — many authors self-post their papers
- arXiv / bioRxiv / SSRN: Search for a preprint of the paper by title or author
- Google Scholar 'All versions': Click 'All versions' under any Google Scholar result — look for PDF links
- Author's university page: Most researchers post their papers on their faculty profile
- Email the author: Authors are always happy to share — a brief email gets a response within days
- University interlibrary loan: Your library can request any paper from another institution, usually within 1-3 days
Frequently asked questions
What is Unpaywall?
Unpaywall is a free browser extension (Chrome and Firefox) developed by OurResearch that automatically finds legal free versions of research papers as you browse. When you visit a publisher's paywall page, Unpaywall checks its database of 50+ million open-access papers and shows a green tab on the right side of the screen if a free version is available. Clicking that tab opens the free PDF directly. Unpaywall only shows legal open-access copies — it doesn't link to pirated versions.
How does Unpaywall find free papers?
Unpaywall searches for legal open-access versions in multiple places: PubMed Central, Europe PMC, arXiv, bioRxiv, institutional repositories (university library servers), author self-archival pages, and journals that offer delayed open access. It checks the DOI against its database and returns the best available free version. The green tab appears within seconds when you visit any paywalled paper page.
Is Unpaywall legal?
Yes — Unpaywall only links to legal open-access versions of papers: preprints deposited by authors, papers in compliance with funder mandates (NIH, Wellcome Trust), papers published in open-access journals, and author manuscripts posted on institutional repositories. It does not link to Sci-Hub or other sites that distribute copyrighted content without permission. Using Unpaywall is fully legal and is endorsed by major libraries and universities.
What percentage of papers can Unpaywall find for free?
According to OurResearch's own data, Unpaywall finds free legal versions for approximately 50% of all scholarly papers. Coverage is highest for biomedical papers (where funder mandates are strong) and computer science/physics (where arXiv preprints are standard). Coverage is lower for humanities and some social science journals. If Unpaywall can't find a paper, try: Semantic Scholar, ResearchGate, emailing the author, or your university library's interlibrary loan service.
Are there alternatives to Unpaywall?
Yes — several complementary tools: Open Access Button (oa.works) does similar searches with a web interface; Kopernio (Clarivate) integrates with reference managers; Google Scholar's 'All versions' links often include free copies; PaperPanda is another browser extension; and Simply the DOI approach: add 'open access' to any Google Scholar search for a paper title. For systematic literature searches, using multiple tools gives the best coverage.