# SiteCheck Web Intel – Unpaywall Open-Access Lookup

> SiteCheck Web Intel – Unpaywall Open-Access Lookup is a paid API for AI agents from api.webintel-api.workers.dev, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-24).

Looks up open-access status and best free full-text link for a paper by DOI using the Unpaywall API

## Facts

- Endpoint: GET https://api.webintel-api.workers.dev/api/search/unpaywall?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-24
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/sitecheck-web-intel-unpaywall-open-access-lookup-ad6fdc94
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_-rEkHzeFW357nmx1AKCNB

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 sitecheck-web-intel-unpaywall-open-access-lookup-ad6fdc94
```

Example prompt: Can you check whether the paper with DOI 10.1038/nature12373 is available open access, and give me the best free link to read it?

## When to prefer this

Use this endpoint when you need to quickly determine whether a specific academic paper (identified by DOI) is freely readable online, and to get the canonical best free full-text URL. Ideal for literature review workflows, citation enrichment, or helping users avoid paywalls. Prefer this over general web search when you have a precise DOI and need structured, reliable OA metadata rather than guessing from search results.

## Known failure modes

- DOI not found in Unpaywall database — returns null or empty OA data
- Invalid or malformed DOI format causes lookup failure
- Paper exists but has no open access version — returns OA status as false with no free link
- Upstream Unpaywall API downtime causes request failure
- Missing or invalid UNPAYWALL_EMAIL configuration on the server side causes rejection

## How this service works

Unpaywall open-access lookup by DOI (free API; it requires a contact e-mail set in UNPAYWALL_EMAIL, not a key): is the paper open access, OA status, best free full-text link, journal and publisher. Returns metadata and links only, not the PDF.

## Output

Returns metadata about the paper identified by the DOI: whether it is open access, the OA type/status (e.g. gold, green, hybrid), the best available free full-text URL, journal name, and publisher. Does not return the PDF itself, only links and metadata.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "doi"
     ],
     "properties": {
      "doi": {
       "type": "string",
       "description": "DOI such as 10.1038/nature12373"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/sitecheck-web-intel-unpaywall-open-access-lookup-ad6fdc94/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.webintel-api.workers.dev](https://www.zero.xyz/host/api.webintel-api.workers.dev/llms.txt)