Check Unpaywall first by DOI to see the open-access locations registered against that exact article, then search CORE by title to find aggregated repository copies, and use whichever route returns a version whose license and version you can legally use and cite. The two routes answer different questions, so they complement each other.
What Unpaywall by DOI tells you
Unpaywall records describe open-access locations associated with a DOI. Each record can include the host type, the version of the article, license information when available, and a selected best open-access location. Because the lookup is keyed to the DOI, it points to locations tied to that specific article rather than to similarly titled works. A DOI resolves through the Handle System to current information supplied for the identified object, commonly a landing page maintained by the registrant, so the DOI is the stable identifier to start from.
What a CORE title search adds
CORE aggregates open-access research outputs and offers discovery services, data access, and tools for finding repository copies of scholarly work. A title search can surface repository copies that are not listed among the DOI's registered open-access locations. Title matching is looser than a DOI lookup, so confirm that a CORE result is the same article (authors, year, journal) before relying on it.
A practical sequence
- Copy the DOI from the paywalled publisher page and query Unpaywall. Result: a list of registered open-access locations with host type, version, and license where available, plus a selected best location.
- Open the best location and check the version and license. Decision point: if the version is one you can use and the license permits your intended use, cite that copy and stop.
- If no usable location appears, search CORE by the article title. Result: candidate repository copies.
- Verify each candidate against the DOI record (authors, year, venue) to confirm it is the same work, then check the version and license shown for that copy.
- Cite the version you actually used, noting the repository or host and the license terms that apply.
Choosing between the results
Use the route that returns a version you can legally use and cite. A registered open-access location with clear license information is the easier case to document; a repository copy found through CORE may still be usable, but confirm its version and any stated license before quoting or redistributing it. If neither route yields a version with terms you can rely on, treat the open-access status as unresolved and check the publisher page or contact the authors for a permitted copy.