# SYNTHORA Unpaywall Open-Access Locator

> 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.

## Facts

- Endpoint: POST https://unpaywall-oa-lookup.hergertsynthora.com/service
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/synthora-unpaywall-open-access-locator-89858c68
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_rIPhjl9e-qgi2Nh3Ae6l7

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability synthora-unpaywall-open-access-locator-89858c68 -d '<json body>'
```

Example prompt: Can you check if there's a free legal PDF available for the paper with DOI 10.1038/nature12373 — I need the open-access URL, license, and where it's hosted?

## When to prefer this

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.

## Known failure modes

- 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- DOI resolves but metadata is incomplete or outdated

## 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.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "doi": {
   "type": "string",
   "description": "doi"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "niche": "unpaywall-oa-lookup",
  "result": {}
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/synthora-unpaywall-open-access-locator-89858c68/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from unpaywall-oa-lookup.hergertsynthora.com](https://www.zero.xyz/host/unpaywall-oa-lookup.hergertsynthora.com/llms.txt)