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

The obvious answer is “Google Scholar” :)  And yup, that works great, and given the resources of Google will probably always be the most comprehensive solution.  But Google’s interface requires an extra search step, and its data isn’t open for others to build tools on top of.

We made a thing to fix that.  Introducing oaDOI:

• DOI gets you a paywall page: doi.org/10.1038/ng.3260
• oaDOI gets you a PDF: oadoi.org/10.1038/ng.3260

We look for open 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.
• Our 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 wonderful 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 the really cool DOAI.  oaDOI is a wrapper around the OA detection used by Impactstory. It’s open source of course, can be used as a lookup engine in Zotero, and has an easy and powerful API that returns license data and other good stuff.

Try it out at oadoi.org, let us know what you think (@oadoi_org), and help us spread the word!