Unpaywall

Unpaywall

Unpaywall is OpenAlex’s Open Access discovery surface: an API, dataset, and browser extension that tell you whether a scholarly article has a free-to-read copy, and where. It’s used by libraries, link resolvers, and thousands of applications.

Unpaywall is not a separate database. Since the Walden rewrite, Unpaywall records are served from the same OpenAlex data that powers everything else — Unpaywall is a legacy-compatible format over that data, kept stable for the large ecosystem built on it. The OA facts in an Unpaywall record and in an OpenAlex work’s open_access object come from the same pipeline.

The Unpaywall surfaces

Surface What it does
REST API api.unpaywall.org/v2/{DOI}?email=you@example.com returns the article’s OA record in the Unpaywall data format
Simple Query Tool Paste up to 1,000 DOIs, get results by email — no code needed
Browser extension Shows a green tab when the article you’re viewing has a free copy
Data feed Change updates in the Unpaywall record format, for subscribers
Link-resolver integrations Unpaywall data inside SFX, EBSCO, 360 Link, and others — see Link resolver integrations

For new projects, consider the OpenAlex API directly — it exposes the same OA information plus everything else OpenAlex knows (works, authors, sources, topics, and more). The Unpaywall format is best when you’re integrating with tools that already speak it.

Which DOIs Unpaywall covers

DOIs can be created by any of several Registration Agencies. The Unpaywall dataset covers articles issued by one: Crossref. If a DOI isn’t in Unpaywall, it might be invalid or created by a different agency — in either case the REST API returns 404, the Simple Query Tool gives a blank row, and it’s absent from the dataset.

  • Check whether a DOI is valid with the doi.org proxy REST API.
  • Check which agency created it with Crossref’s agency endpoint: https://api.crossref.org/works/{DOI}/agency.
  • Some valid Crossref DOIs are still excluded because they’ve been deleted or are used for testing.

DataCite DOIs aren’t included. Nearly everything with a DataCite DOI is Open Access, so classifying them added little value and was mostly a source of errors — for statistical purposes, if you have a DataCite DOI, it’s OA. (OpenAlex itself does index DataCite works — that’s one of the things the OpenAlex API gives you beyond the Unpaywall format.)

Fixing errors

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