Query Unpaywall with the paper's DOI to retrieve the open-access locations associated with that DOI, then use CORE or DOAJ to locate repository or open-access journal copies.
Unpaywall records describe open-access locations tied to a DOI, including host type, version, license information when available, and a selected best open-access location. That record gives you candidate copies to inspect rather than a single fixed answer.
- Run the DOI through Unpaywall and read the returned locations. Expect a list of open-access locations plus a selected best location; use the best location as your first candidate and the remaining entries as alternates.
- Check each candidate's host type, version, and license fields before relying on it. The host type tells you where the copy sits, the version tells you which manuscript stage it represents, and the license field, when present, tells you what reuse the copy permits.
- If Unpaywall returns no usable location, search CORE for repository copies of the work. CORE aggregates open-access research outputs and offers discovery services and tools for finding repository copies of scholarly work.
- For papers published in open-access journals, search DOAJ for the article and journal record. DOAJ provides searchable article and journal records for open-access journals that meet its inclusion criteria.
A missing location in one route leaves the question unresolved; move to the next route and compare what each source returns. When a record lists several locations, the selected best location is a starting point for inspection, and the version and license fields decide whether a given copy fits your use.