Unpaywall
- Free allowance
- The REST API is free, with up to 100,000 calls per day and an email address as a query parameter; there is no key.
- Verdict
- ★ qualifiesusable as stated; the read path was probed
- Cost
- free tier
- Identity
- anonymousno card, no phone
- Binding limit
- request-rate100,000 calls per day; no per-second rate published
- Evidence
- documented38 sources; a first-party page was read and the sentence quoted
- Freshness
- stale on 2026-12-04checked 2026-11-03 (live); stale on 2026-12-04
| Free tier | The REST API is free, with up to 100,000 calls per day and an email address as a query parameter; there is no key. Unpaywall no longer makes its own snapshots; the same data is in the OpenAlex public snapshot, free to download from S3 with no AWS account. unit requests; metered on request-count; The 100,000 figure is a stated limit on use, not a measured cutoff; no per-second rate is published. DOI lookup is the only API endpoint: title search was retired on 2026-09-18 and answers 410. Unpaywall runs on the OpenAlex database since late 2025. |
|---|---|
| Price | none stated |
| Limits |
A call without an email parameter answered 422. The search endpoint answers 410 since 2026-09-18. |
| Binding | request-rate At 100,000 calls a day, polling the whole DOI space through the API takes many months, so a whole-corpus read goes to the OpenAlex snapshot, which has no request count. |
| Identity | anonymous No account and no key: each call carries an email address as a query parameter, and a call without one answered 422. The example address in the documentation answered 200, so no account stands behind the address. The OpenAlex S3 snapshot needs no AWS account. The Data Feed is paid and priced by quote. |
| Egress | Free: API responses carry no byte price; the OpenAlex S3 bucket is free to download with no AWS account, the data-transfer fees covered by the AWS Open Data program free allowance: no byte allowance published |
| Per-object cap | one DOI per API call; the Simple Query Tool takes up to 1,000 DOIs per batch and returns results by email |
| Retention | the API answers from the live database; Unpaywall snapshots are no longer created; the OpenAlex public snapshot is a point-in-time release, quarterly, on the second Wednesday of January, April, July and October |
| Interface | rest, s3 GET https://api.unpaywall.org/v2/{DOI}?email=ADDRESS returns one JSON DOI object; bulk: the OpenAlex bucket s3://openalex/data/ read with --no-sign-request, JSON Lines about 745 GB and Parquet about 770 GB as of the September 2026 release; the paid Data Feed serves daily and weekly changefiles and a daily snapshot with an API key. endpoint: https://api.unpaywall.org/v2/ |
| Tooling | Any HTTP client for the API; the AWS CLI (aws s3 sync with --no-sign-request) or any S3 client for the OpenAlex snapshot. |
| Composes with | Per-DOI lookups go to the Unpaywall API at up to 100,000 a day; a whole-corpus read goes to the OpenAlex public snapshot on S3, whose open_access and best_oa_location fields carry the same values; search goes to the OpenAlex API. |
| Reliability | Title search was retired on 2026-09-18 and answers 410; the DOI lookup API and the Data Feed are stated to stay. Unpaywall-format snapshots are no longer made, so a bulk copy is in the OpenAlex format. |
| Notes | Bulk path: the OpenAlex public snapshot (s3://openalex, unsigned), which carries the Unpaywall open-access fields in the OpenAlex format; the Unpaywall-format daily snapshot is part of the paid Data Feed. |
| Evidence note | documented The daily figure is documented, not exhausted. A DOI lookup with an email answered 200, one without answered 422, the search endpoint answered 410, and an anonymous listing of the OpenAlex bucket answered 200. |
| Parsed numbers |
|
Evidence 38
| date | source | what it proved |
|---|---|---|
| 2026-10-30 | unpaywall.org/products/api | part of the text of Free tier, above |
| 2026-10-30 | unpaywall.org/products/api | each request carries an email address as a URL parameter |
| 2026-10-30 | unpaywall.org/products/api | the API is limited to 100,000 calls per day |
| 2026-10-30 | unpaywall.org/products/api | the documented bulk path is a full snapshot |
| 2026-10-30 | unpaywall.org/products/api | the search endpoint was retired on 18 September 2026 |
| 2026-10-30 | unpaywall.org/products/api | v2 is the only supported version |
| 2026-10-30 | probe: https://api.unpaywall.org/v2/10.1038/nature12373?email=unpaywall_01@example.com | a DOI lookup with an email parameter and no account answered 200 |
| 2026-10-30 | probe: https://api.unpaywall.org/v2/10.1038/nature12373 | a DOI lookup with no email parameter is refused |
| 2026-10-30 | probe: https://api.unpaywall.org/v2/10.1038/nature12373 | the refusal is HTTP 422 |
| 2026-10-31 | probe: https://api.unpaywall.org/v2/search?query=cell%20thermometry&email=unpaywall_01@example.com | the search endpoint answered 410 with its retirement date |
| 2026-10-30 | unpaywall.org/products/snapshot | Unpaywall no longer creates its own snapshots |
| 2026-10-30 | unpaywall.org/products/snapshot | the Unpaywall page states a monthly OpenAlex snapshot |
| 2026-10-30 | unpaywall.org/products/data-feed | the Data Feed is paid |
| 2026-10-30 | unpaywall.org/products/data-feed | the Data Feed is priced by quote |
| 2026-10-30 | unpaywall.org/products/data-feed | a daily Unpaywall-format snapshot comes only with the paid Data Feed |
| 2026-10-30 | unpaywall.org/products/data-feed | part of the text of Binding, above |
| 2026-10-30 | help.openalex.org/access/unpaywall/ | Unpaywall runs on the OpenAlex database since late 2025 |
| 2026-10-30 | help.openalex.org/access/unpaywall/ | the OpenAlex snapshot carries the same open-access values |
| 2026-10-30 | help.openalex.org/access/unpaywall/ | part of the text of Reliability, above |
| 2026-10-30 | help.openalex.org/access/unpaywall/ | the Simple Query Tool takes up to 1,000 DOIs per batch |
| 2026-10-30 | help.openalex.org/access/unpaywall/ | only Crossref DOIs are covered |
| 2026-10-30 | help.openalex.org/access/unpaywall/ | a DOI outside the dataset answers 404 |
| 2026-10-30 | developers.openalex.org/download/snapshot-format | the OpenAlex snapshot bucket is free with no AWS account |
| 2026-10-30 | developers.openalex.org/download/snapshot-format | the snapshot is read with an unsigned S3 sync |
| 2026-10-30 | developers.openalex.org/download/snapshot-format | the JSON Lines snapshot is about 745 GB compressed |
| 2026-10-30 | developers.openalex.org/download/snapshot-format | the Parquet snapshot is about 770 GB compressed |
| 2026-10-30 | developers.openalex.org/download/snapshot-format | the sizes are those of the September 2026 release |
| 2026-10-30 | developers.openalex.org/download/snapshot-format | the free public snapshot is released quarterly |
| 2026-10-30 | developers.openalex.org/download/snapshot-format | the AWS Open Data program pays the transfer fees |
| 2026-10-31 | probe: https://openalex.s3.amazonaws.com/?list-type=2&prefix=data/jsonl/works/&max-keys=3 | an unsigned listing of the openalex bucket answered 200 with object keys |
| 2026-10-31 | probe: https://openalex.s3.amazonaws.com/?list-type=2&prefix=data/jsonl/works/&max-keys=3 | the works manifest in the bucket was last modified on 2026-10-14 |
| 2026-11-02 | help.openalex.org/access/sync/ | the OpenAlex sync page names itself the authoritative reference for when releases happen |
| 2026-11-02 | help.openalex.org/access/sync/ | the free public snapshot is released quarterly on the second Wednesday of January, April, July and October |
| 2026-11-02 | help.openalex.org/access/sync/ | the next public release is dated 2027-01-13 |
| 2026-11-02 | openalex.s3.amazonaws.com/RELEASE_NOTES.txt | the release notes header states the quarterly schedule |
| 2026-11-02 | probe: https://openalex.s3.amazonaws.com/data/jsonl/manifest.json | the combined JSON Lines manifest of the public bucket is dated 2026-10-14 |
| 2026-11-02 | unpaywall.org/products/snapshot | the Unpaywall snapshot page still says the OpenAlex snapshot is updated approximately once per month |
| 2026-11-02 | unpaywall.org/products/snapshot | Unpaywall no longer creates its own snapshots |