Where to read research papers for free, legally

By Koray Özcan · Updated October 10, 2026

Most research papers have a free, legal copy somewhere: a preprint server, a university repository, a government archive or the author's own page. The fastest way to find it is to search by the paper's DOI with an open-access tool such as Unpaywall or OpenAlex, then try the sources below in order. You almost never need a pirate site.

Start with the DOI

Every published paper has a DOI, a permanent identifier that looks like `10.1038/nature12373`. Open-access tools use it to find every legal copy of the paper at once, so copy it from the publisher's page before you start.

Eight legal places to look

1. Unpaywall. A free browser extension that shows a green tab when a legal free copy of the paper you are viewing exists (Unpaywall).
2. OpenAlex. An open catalog of over 250 million scholarly works. Each record lists its open-access locations, including the free PDF (OpenAlex).
3. arXiv. Preprints in physics, mathematics, computer science, statistics, economics and more, all free (arXiv).
4. bioRxiv and medRxiv. Preprints in biology and medicine. Check whether a later published version changed the findings (bioRxiv, medRxiv).
5. PubMed Central and Europe PMC. Free full texts of biomedical papers, including many funded by public money (PubMed Central, Europe PMC).
6. CORE. Full texts from thousands of university repositories worldwide (CORE).
7. The author's own page. Many researchers post their accepted manuscripts on their personal or university pages. Google Scholar's "All versions" link often finds them.
8. Ask the author. Email the corresponding author for a copy. Most are glad someone wants to read their work.

Preprint, accepted manuscript or published version?

A free copy is not always the final one. A preprint is the version before peer review. An accepted manuscript has passed peer review but lacks the journal's formatting. The published version is the journal's final copy. For most reading, an accepted manuscript is as good as the published version; for preprints, check whether the paper was later published and whether anything changed.

If you are at a university

Your library pays for many journals. Sign in through your library's website, use a browser tool your library recommends, or ask for an interlibrary loan for anything it does not hold.

How Nerdi finds free PDFs

Nerdi is an iPhone app that shows three research papers a day. It reads each paper's open-access locations from OpenAlex and only labels a paper "Free PDF" when a legal copy exists, opening it right in the app. Its field pages list new papers with free PDFs in 20 fields.

Written by the developer of Nerdi, one of the apps mentioned.