eduKateSG · Why Science?
The best free route is still a particular copy with a particular version
Read Unpaywall and its shared OpenAlex access data through DOI lookups, OA locations, host type, manuscript version, licence, best-location ranking and retrieval dates.
Finding a paper can be harder than understanding its title. A publisher page may be paywalled while an accepted manuscript is freely available in an institutional repository. Unpaywall was built to answer a focused question: is there a free, legal copy of a DOI-identified paper?
As of the official September 2026 product documentation, Unpaywall and OpenAlex run on the same underlying database. The Unpaywall API remains a legacy-compatible DOI-in, open-access-answer-out interface, while OpenAlex exposes the same access evidence within a wider scholarly graph.
Did you know? One paper can have several open locations. A best open-access location is selected by ordered preferences that include publisher versus repository hosting, version, presence of a direct PDF, match quality and repository ranking. Best means preferred by those rules, not scientifically superior.
This guide separates access from evaluation. An open URL can help a learner read the work, but it does not guarantee peer review, a permissive reuse licence, the version of record, complete supplementary files or a correct conclusion.
Chapter index
Chapters 1–9: DOI lookup, OA status and locations
- 1. The DOI anchors the lookup
- 2. The legacy interface has a focused job
- 3. The database is shared with OpenAlex
- 4. OA status summarises availability
- 5. Locations are individual copies
- 6. Publisher and repository hosts differ
- 7. Versions matter for quotation
- 8. Best location follows ranking rules
- 9. A PDF URL is not a licence
Chapters 10–17: versions, licences, dates and integration limits
- 10. Licences can be missing or restrictive
- 11. Bronze availability can change
- 12. Repository dates need interpretation
- 13. Closed means no known open copy
- 14. The extension depends on page metadata
- 15. Link resolvers add another hand-off
- 16. Access records can change
- 17. Open-access literacy supports careers
Open access is a property of a particular copy and route, not a guarantee about scientific quality. Unpaywall looks up scholarly works by DOI. A DOI must identify the paper itself rather than merely appear somewhere on a related webpage. This separates finding a lawful free copy from judging its research.
Try this
Evidence question: Which DOI belongs to this article? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Resolve the DOI before querying the access record. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Keep the identifier, retrieval date and source page in the note so the route can be repeated.
Evidence checkpoint
Record the evidence object for the doi anchors the lookup, its identifier or version context, and one limit that must remain visible.
One work may have publisher, accepted-manuscript and submitted-manuscript locations. The Unpaywall REST API returns an OA record for a DOI in a stable format used by many integrations. Broader search and graph analysis belong in OpenAlex. It also keeps version, host and licence attached to the chosen document.
Try this
Evidence question: Is the task a DOI lookup or literature search? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Choose the surface that matches the question. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. If a field is missing, write “not shown” and follow the official documentation rather than inventing a value.
Evidence checkpoint
Record the evidence object for the legacy interface has a focused job, its identifier or version context, and one limit that must remain visible.
A best location is a ranked convenience choice whose version and licence still need reading. Official change notes say Unpaywall and OpenAlex now use one underlying dataset. Fields such as is_oa, oa_status and the best PDF route align across the two representations. A learner can reach the text quickly without flattening every copy into the version of record.
Try this
Evidence question: Are two interfaces showing the same underlying work? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Compare the DOI and location fields rather than assuming separate coverage. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Before comparing two records, check that their object types, methods, versions and units really align.
Evidence checkpoint
Record the evidence object for the database is shared with openalex, its identifier or version context, and one limit that must remain visible.
A DOI lookup can return useful access evidence while leaving the paper’s claims unevaluated. The access record classifies a work as diamond, gold, green, hybrid, bronze or closed under the service’s rules. Status is a summary and can hide multiple locations. The result is an access receipt that remains honest about what was found.
Try this
Evidence question: Which location evidence produced the status? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Open the full locations list before reporting the label. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Finish by naming one supported statement and one stronger statement that still needs another evidence layer.
Evidence checkpoint
Record the evidence object for oa status summarises availability, its identifier or version context, and one limit that must remain visible.
Open access is a property of a particular copy and route, not a guarantee about scientific quality. Each location describes where a copy is hosted, with landing-page, PDF, licence, version and source information when detected. Different locations may expose different manuscripts. This separates finding a lawful free copy from judging its research.
Try this
Evidence question: Which copy did you actually read? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Save the exact location URL and host. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Keep the identifier, retrieval date and source page in the note so the route can be repeated.
Evidence checkpoint
Record the evidence object for locations are individual copies, its identifier or version context, and one limit that must remain visible.
One work may have publisher, accepted-manuscript and submitted-manuscript locations. A publisher-hosted location comes from the publishing route, while repository locations include institutional and subject repositories. Host type does not by itself determine manuscript version. It also keeps version, host and licence attached to the chosen document.
Try this
Evidence question: Who maintains this location? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Record source type and name separately. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. If a field is missing, write “not shown” and follow the official documentation rather than inventing a value.
Evidence checkpoint
Record the evidence object for publisher and repository hosts differ, its identifier or version context, and one limit that must remain visible.
A best location is a ranked convenience choice whose version and licence still need reading. Locations may be labelled submittedVersion, acceptedVersion or publishedVersion. Layout and editorial changes can differ even when the study is recognisably the same. A learner can reach the text quickly without flattening every copy into the version of record.
Try this
Evidence question: Which version contains the quoted text or figure? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Put version beside page or section details. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Before comparing two records, check that their object types, methods, versions and units really align.
Evidence checkpoint
Record the evidence object for versions matter for quotation, its identifier or version context, and one limit that must remain visible.
A DOI lookup can return useful access evidence while leaving the paper’s claims unevaluated. The preferred OA location is selected using host, version, PDF availability, matching and repository tiebreakers. A different research purpose may justify another location. The result is an access receipt that remains honest about what was found.
Try this
Evidence question: Why was this copy ranked best? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Compare the winner with at least one alternative. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Finish by naming one supported statement and one stronger statement that still needs another evidence layer.
Evidence checkpoint
Record the evidence object for best location follows ranking rules, its identifier or version context, and one limit that must remain visible.
Open access is a property of a particular copy and route, not a guarantee about scientific quality. Direct file access says where bytes can be retrieved. Reuse rights depend on an explicit licence or other lawful permission. This separates finding a lawful free copy from judging its research.
Try this
Evidence question: What may the reader do beyond reading? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Open the licence URI before planning redistribution. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Keep the identifier, retrieval date and source page in the note so the route can be repeated.
Evidence checkpoint
Record the evidence object for a pdf url is not a licence, its identifier or version context, and one limit that must remain visible.
CHAPTER 10 OF 17 · Read versions and licences
10. Licences can be missing or restrictive
One work may have publisher, accepted-manuscript and submitted-manuscript locations. The service records recognised licences and may return null or an implied-open label when no specific licence is identified. Free-to-read does not automatically mean unrestricted reuse. It also keeps version, host and licence attached to the chosen document.
Try this
Evidence question: Is the permission explicit, inferred or absent? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Write the access and reuse statements separately. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. If a field is missing, write “not shown” and follow the official documentation rather than inventing a value.
Evidence checkpoint
Record the evidence object for licences can be missing or restrictive, its identifier or version context, and one limit that must remain visible.
A best location is a ranked convenience choice whose version and licence still need reading. Bronze describes free access on a toll-access publisher without a recognised open licence under the current taxonomy. Availability can be temporary. A learner can reach the text quickly without flattening every copy into the version of record.
Try this
Evidence question: Could this route disappear or change? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Record retrieval date and avoid promising permanent access. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Before comparing two records, check that their object types, methods, versions and units really align.
Evidence checkpoint
Record the evidence object for bronze availability can change, its identifier or version context, and one limit that must remain visible.
CHAPTER 12 OF 17 · Read versions and licences
12. Repository dates need interpretation
A DOI lookup can return useful access evidence while leaving the paper’s claims unevaluated. OA dates for repository copies can reflect when records were first observed rather than the exact deposit moment, especially for older material. The result is an access receipt that remains honest about what was found.
Try this
Evidence question: Which event does oa_date describe? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Do not substitute it for publication or acceptance date. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Finish by naming one supported statement and one stronger statement that still needs another evidence layer.
Evidence checkpoint
Record the evidence object for repository dates need interpretation, its identifier or version context, and one limit that must remain visible.
Open access is a property of a particular copy and route, not a guarantee about scientific quality. A closed result means the current system has not identified a qualifying free location. It does not prove that no lawful copy exists anywhere. This separates finding a lawful free copy from judging its research.
Try this
Evidence question: Which repositories or author pages remain to check? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Describe the result as no known location on the access date. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Keep the identifier, retrieval date and source page in the note so the route can be repeated.
Evidence checkpoint
Record the evidence object for closed means no known open copy, its identifier or version context, and one limit that must remain visible.
CHAPTER 14 OF 17 · Use the route responsibly
14. The extension depends on page metadata
One work may have publisher, accepted-manuscript and submitted-manuscript locations. The browser extension finds a page’s DOI through recognised HTML metadata fields. A missing or incorrect tag can prevent a correct lookup. It also keeps version, host and licence attached to the chosen document.
Try this
Evidence question: Did the page expose its own DOI? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Inspect the metadata and avoid borrowing a related item’s DOI. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. If a field is missing, write “not shown” and follow the official documentation rather than inventing a value.
Evidence checkpoint
Record the evidence object for the extension depends on page metadata, its identifier or version context, and one limit that must remain visible.
A best location is a ranked convenience choice whose version and licence still need reading. Library systems can use Unpaywall redirects or API data to send readers to open copies. Routing errors may arise in the source data or in the local resolver integration. A learner can reach the text quickly without flattening every copy into the version of record.
Try this
Evidence question: Which system chose the final URL? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Keep the original DOI and redirect chain for troubleshooting. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Before comparing two records, check that their object types, methods, versions and units really align.
Evidence checkpoint
Record the evidence object for link resolvers add another hand-off, its identifier or version context, and one limit that must remain visible.
A DOI lookup can return useful access evidence while leaving the paper’s claims unevaluated. Repositories add manuscripts, publishers change pages and licences are corrected. A live lookup should therefore carry a retrieval date. The result is an access receipt that remains honest about what was found.
Try this
Evidence question: Has the chosen location or version changed? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Repeat the DOI lookup before final submission. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Finish by naming one supported statement and one stronger statement that still needs another evidence layer.
Evidence checkpoint
Record the evidence object for access records can change, its identifier or version context, and one limit that must remain visible.
CHAPTER 17 OF 17 · Use the route responsibly
17. Open-access literacy supports careers
Open access is a property of a particular copy and route, not a guarantee about scientific quality. Librarians, repository managers, publishers, developers and open-science analysts maintain routes from identifiers to lawful copies. This separates finding a lawful free copy from judging its research.
Try this
Evidence question: Which role fixes a wrong DOI-to-PDF match? Answer in three parts: identify the visible field or file, explain how it bears on the question, and state the boundary of that evidence. Preserve the database’s own object names and accession rather than flattening everything into the word ‘data’.
Try this: Create an access receipt for a school research source. Turn the result into a compact claim-evidence-reasoning note, then ask a partner to retrace it. Keep the identifier, retrieval date and source page in the note so the route can be repeated.
Evidence checkpoint
Record the evidence object for open-access literacy supports careers, its identifier or version context, and one limit that must remain visible.
Contents · Previous chapter · Continue at the Science Learning Hub
Open the best route, then name the copy you used
Unpaywall provides a direct route from DOI to known open-access evidence in a familiar record format. Its value grows when locations, versions, hosts and licences remain visible.
Save the DOI, is_oa status, selected location, host type, manuscript version, licence, redirect path and lookup date. Then evaluate the paper’s methods and current publication status separately.
| Reading object | What it can support | Question to keep visible |
|---|---|---|
| DOI | Identity used for lookup | Does it name this paper? |
| OA location | A freely readable copy | Who hosts it and which version is it? |
| Licence | Reuse permission evidence | Is it explicit? |
| Best-location rule | Service ranking of copies | Does the research task need another copy? |
Sources and next reading
Substantive resource claims in this article were checked against the primary pages below. A structured record is a route into evidence; it does not by itself prove a scientific conclusion. Recheck the live record, evidence labels and release context before using it in assessed work or research.
For a classroom enquiry, save a short research receipt containing the question, search terms, selected object, exact identifier, version, access date and the evidence boundary you observed. Add the file or page that supports each statement. This small routine turns browsing into accountable science learning and gives a teacher, classmate or future analyst a route they can independently follow.
Before sharing the conclusion, ask another reader to retrace the route without verbal hints. If they reach a different version, file or interpretation, improve the receipt and narrow the claim. Reproducibility begins with this practical check. It teaches careful reading, supports fair collaboration and keeps uncertainty visible while evidence moves from an online service into notes, analysis and a final explanation.
A useful final review separates five questions. What object was found? Which organisation or repository maintains it? What exact evidence was inspected? Which statement does that evidence support? What remains uncertain? Answer each question in one sentence, then connect every answer to a visible field, file or source page. This review catches common mistakes: citing a collection when a file supplied the value, treating the newest release as the analysed release, confusing permission with scientific suitability, or turning a discovery count into a conclusion. It also gives students a calm way to improve work. A missing detail becomes a next research step instead of an invitation to guess. When the route is complete, the final explanation can stay simple because the identifiers, dates, versions, limitations and supporting evidence are already organised underneath it.
Primary sources
- Unpaywall product change notes — accessed 25 October 2026.
- Open-access locations and licences — accessed 25 October 2026.
- Repository harvesting and version reporting — accessed 25 October 2026.
- Link-resolver integrations — accessed 25 October 2026.
- OpenAlex work attributes used by Unpaywall — accessed 25 October 2026.