Unpaywall is a free browser extension for Firefox and Chrome that allows you to read research papers behind paywalls for free legally.
The extension works identical in both browsers. Whenever you hit a research paper paywall on the web that asks you to pay up to read the whole paper, a query is run in the background to check whether a copy of the research paper is already available in a free index.
If that is the case, that is indicated to you in the browser. All it takes then is to click on an icon in the browser to read the paper for free, legally,
The maintainers state that the index has over 10 million entries already, and that the system finds fulltext for 65% to 85% of research articles. The service relies on several databases and data sources such as PubMed Central, the DOAJ, Google Scholar or BASE, and that all these are made available via an API.
Unpaywall is not the first service that you may use to find free copies of research papers that are locked behind a payway. The OA Button extension for Chrome comes closest probably. While it handles things a bit different -- you click on the extension's icon to run a search, and may use a couple of extra features such as a search form on the project website or requests -- it runs similar queries in the background.
Unpaywall is more hands-off as it runs the scan for a free copy of a research paper automatically, but it lacks the advanced features that OA Button offers.
The browser extension ships with two options thought that you can enable on the preferences page. Click on the extension icon and select settings to open the preferences.
If you read research papers, either because you are in academia, a student, or interested in the subject, then you may like what the browser extension has to offer. Its growing index of research paper copies provides you with free legal access to articles behind paywalls.
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