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Open Access

From Paywalled to OA Versions

More and more funders and universities require their authors to upload an OA version of their papers onto repositories. It means that, for many paywalled articles, there is also an OA version somewhere. Several (fully legal) tools have been built to help readers to find them.

OA Only Tools


  • Unpaywall is an open-source and nonprofit browser extension (Firefox and Chrome) which searches automatically for OA versions of articles. It is also possible to query the database directly: you must give your email address, and then you receive a report with the URL of the best open-access version. 
    Unpaywall is integrated within Zotero: if Zotero can not access the publisher's version of an article and attach it to the reference, it uses Unpaywall to search for an open-access version instead. 
  • The Open Access Button website allows searching for OA versions of articles. If it is not possible to find an OA version, they ask the author to share it by putting it in a repository. It is open-source, non-profit, and has been launched in 2013. There are also Firefox and Chrome browser extensions.
  • Open Access Helper allows Safari users (on desktop or mobile devices) to find OA versions of articles. There are also Firefox and Chrome browser extensions.

Tool for OA and Paywalled Versions

  • Endnote Click (formerly Kopernio) is a browser extension for Firefox, Chrome, and Edge that finds the "best" (the final published version when possible) PDF version of an article, in OA repositories or using the user's university subscription. A "locker" allows storing previously accessed papers.
  • Google Scholar searches automatically open access or paywalled versions of articles. 

OA Aggregators

These tools provide a search platform for open access research outputs from repositories and journals worldwide.

OA Directories