The Open Access DOI

Many papers that are free-to-read are available thanks to “green Open Access” copies posted in institutional or subject repositories. The fact these copies are available for free is great because anyone can read the research, but it does present a major challenge: given the DOI of a paper, how can you find the open version, given there are so many different repositories?

oaDOI is hoping to fix that:

  • the DOI will often get you a paywall page
  • the oaDOI gets you a PDF


aoDOI looks for open access copies of articles using the following data sources:

  • The Directory of Open Access Journals to see if it’s in their index of OA journals.
  • CrossRef’s license metadata field, to see if the publisher has reported an open license.
  • Own custom list DOI prefixes, to see if it’s in a known preprint repository.
  • DataCite, to see if it’s an open dataset.
  • The BASE OA search engine to see if there’s a Green OA copy of the article. BASE indexes 90mil+ open documents in 4000+ repositories by harvesting OAI-PMH metadata.
  • Repository pages directly, in cases where BASE was unable to determine openness.
  • Journal article pages directly, to see if there’s a free PDF link (this is great for detecting hybrid OA).

oaDOI was inspired by DOAI. oaDOI is a wrapper around the OA detection used by Impactstory. It’s open source, can be used as a lookup engine in Zotero, and has an easy and powerful API that returns license data.

Try it out at and let them know what you think (@oadoi_org)!


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