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SYNTHORA Unpaywall Open-Access Locator
x402
SYNTHORA Unpaywall Open-Access Locator is a paid API for AI agents from unpaywall-oa-lookup.hergertsynthora.com, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).
Given a DOI, returns whether a legal open-access PDF copy exists, along with the best OA URL, host type, license, version, and repository metadata via the Unpaywall data source.
Price / call$0.001
Success—
StatusUnknown
How this service works
Given a DOI, Unpaywall returns whether a legal open-access copy exists plus the best OA PDF URL, host type, license, version and repository as JSON (keyless with an email parameter). Essential for autonomous research agents and agent-to-agent workflows fetching legally free full text. First 3 calls FREE per wallet — send header X-WALLET: 0x<addr>. No charge on upstream failure.
Output
A JSON object indicating whether an open-access copy exists (ok/true), the best OA PDF URL, the host type (e.g. repository, publisher), the license (e.g. CC BY), the version (e.g. acceptedVersion, publishedVersion), and the repository name. Returns structured metadata suitable for automated full-text retrieval pipelines.
Example use cases
Full-text retrieval for literature review
“I'm doing a systematic review and need to know if the paper at DOI 10.1016/j.cell.2020.02.052 has a free legal PDF I can download — can you find the best open-access link and tell me what license it's under?”
Paywall check before purchasing access
“Before I pay for access to this article, can you check if DOI 10.1126/science.aab3642 is available somewhere for free and legal? If so, give me the direct PDF URL.”
Automated OA enrichment for citation database
“For each paper in my citation list, starting with DOI 10.1093/bioinformatics/bty560, can you look up whether there's an open-access version and return the host type, version, and PDF URL so I can build a freely accessible reading list?”
Technical details
Endpoint
POSThttps://unpaywall-oa-lookup.hergertsynthora.com/serviceWhen to prefer
Choose this endpoint when you need to programmatically determine whether a specific academic paper has a freely and legally accessible full-text version, especially in agentic research workflows where manual library access is not possible. It is ideal for automating literature retrieval, building open-access reading lists, or verifying free availability before purchasing journal access. Prefer this over general web search when you need structured, reliable OA metadata including license and version information sourced from the Unpaywall database.
Side effects
- DOI not found in Unpaywall database — returns ok:false or empty result
- Malformed DOI input causing lookup failure
- Paper exists in Unpaywall but has no open-access copy — returns ok:true with null OA URL
- Service unavailable or payment failure resulting in HTTP error
- DOI resolves but metadata is incomplete or outdated
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| doi | string | doi |
Output
Schema · Response
{
"type": "json",
"example": {
"ok": true,
"niche": "unpaywall-oa-lookup",
"result": {}
}
}Tags
x402
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