No more paywalls: Find the full-text of an article for free using Unpaywall


Last week, Impactstory released a trial version of Unpaywall- a highly anticipated tool that links you to free full-text  articles as you browse the Internet. In other words, a one-stop-shop for open access articles. I downloaded Chrome on my Mac  at home just to try it out (currently, the extension only works in Chrome and Firefox). Here’s some more information, a few of my initial thoughts, and the results of my own personal research study.

What is Unpaywall?

Unpaywall is an extension that allows you to find open access versions of paywalled research papers as you browse the web. Just click on the tab and it will take you to the full-text if available- free, easy to use, and 100% legal.


Unpaywall extension in Chrome



A green tab means that the full-text is available (click on the tab to go to the full-text); a grey tab means that there is no full-text available



Full-text article


How many articles are currently indexed in Unpaywall?

According to Unpaywall’s website,  over 10 million legal open access articles are currently available.

Where do the articles come from?

The articles have either been published in an open access journal (Gold open access) or they are full-text PDFs that authors have uploaded to institutional repositories, subject repositories, or preprint servers (Green open access). Unpaywall relies on open data services freely available on the web, such as PubMed Central. DOAJ, and Crossref, Datasite, and BASE. After pulling all of this data, Unpaywall uses the article’s DOI number and searches a number of sources for an OA version that article. In this way, it is very similar to oaDOI- a tool that searches for an open access version of an article using the  digital object identifier for that article (DOI). However, unlike oaDOI, where you have to enter the DOI manually into a search box, Unpaywall performs this search while running in the background – basically eliminating a step.

How is Unpaywall different from #icanhazpdf or Sci-Hub?

The major difference between Unpaywall and #icanhazpdf or Sci-Hub is that Unpaywall’s method of getting full-text articles is perfectly legal. Unlike Sci-Hub, which is currently facing a multi-million dollar lawsuit due to copyright infringement, Unpaywall finds copies of articles that are published in open access journals or that authors have chosen to share via institutional repositories, subject repositories, or preprint servers. In addition to working with, rather than against, copyright laws, the other great thing about Unpaywall is that, by choosing to use it, you are helping to support the Open Access movement. Traditionally, it has been hard to locate open access articles. Unpaywall is tool that streamlines this process by making open access articles more discoverable to researchers.

How often is Unpaywall able to find the full-text of an article you are looking for?

On their website, Impactstory claims a nearly 50% success rate- a percentage that varies by year and by subscription. However, the creators predict greater success, as more and more papers are made open access with recent open access mandates in the United States and the Tri-Agency Open Access Policy right here in Canada.

Sounds great right? But does Unpaywall actually work as well as the Impactstory claims? To find out, I tested this statistic myself using articles from  Almetric’s Top 100 Articles of 2016 and good ol’ Google Scholar. Here’s what I found…


Every year, Altmetric releases a top-100 list of the most-discussed articles. Of the articles listed in Altmetric’s Top 100 Articles 2016, roughly 30% of the articles were published under a Gold open access license– meaning that they were published in an open access journal (See Figure 1). Altmetric states that this number is higher than in past years.

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Figure 1. Of the one hundred articles in Altmetrics’s Top 100 2016, roughly 70%  were not published in an open access journal; 30% were published in an open access journal

Unpaywall found copies of these Gold open access articles over 80% of the time and had about a 20% failure rate (see Figure 2). Hopefully, this failure rate will improve after Impactstory works out a few initial growing pains.***

***Note: The DOIs for the missing Gold articles have since been fixed by Unpaywall. ***


Figure 2. Percentage of Gold OA articles where a full-text version was found by Unpaywall


However, the results get even more interesting. Of the 69 articles that were not published in an open access journal (aka articles that would normally be hidden behind a paywall), Unpaywall was able to find a full-text version for 25 of these articles. That’s 36% more articles that are freely available to you thanks to Unpaywall (See Figure 3). These articles were self-archived, meaning that they were uploaded by the author(s) to an institutional repository, subject repository, or to a preprint server. In other words, these are Green open access articles.



Figure 3. Percentage of full-text found for articles that were not published in an open access journal


Overall, my results match the 50% success rate claimed by Impactstory. Of the 100 articles in Altmetric’s Top 2016 list, Unpaywall found a full-text copy 53% of the time (53 full-text articles were found; 47 articles no full-text found).

In summary, Unpaywall is a great tool for finding full-text versions of articles with a few shortcomings. If you haven’t given the tool a try already, I’d highly recommend testing it out before its official April 4th release date.

Tool at a Glance:


  • Easy to install and use
  • Works seamlessly in the background- no extra steps needed
  • Colour coding option for tab allows you to differentiate between Gold OA articles and Green OA articles
  • Found full-text versions of articles over 50% of the time
  • Found full-text versions of articles that were previously behind paywalls (not published OA) or not as easy to find


  • Extension is only available currently for Chrome and Firefox
  • Some articles that were published in open access journals were not found
  • No way to store, cite, or share articles once found