# Open-Access PDF Locator for DOI

> Open-Access PDF Locator for DOI is a paid API for AI agents from api.agentstools.dev, paid per call via x402, $0.008/call, status unknown (last checked 2026-10-12).

Given a DOI, returns whether a free open-access PDF exists and provides the best PDF link with its license, version, and host type via Unpaywall and OpenAlex.

## Facts

- Endpoint: GET https://api.agentstools.dev/scholar/oa?utm_source=zero.xyz
- Price: $0.008/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/open-access-pdf-locator-for-doi-9491ea93
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Uzc_vnbiikyVvRk9KB-zG

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 open-access-pdf-locator-for-doi-9491ea93
```

Example prompt: Can you check if there's a free open-access PDF available for the paper with DOI 10.1038/s41586-021-03819-2 — I need the download link, the license, and whether it's a preprint or the published version?

## When to prefer this

Use this endpoint when you have a specific DOI and need to quickly determine if a free, legal PDF is available and where to get it. It is cheaper and more focused than a full paper metadata resolver — ideal when the only goal is OA availability and download URL, not full bibliographic enrichment.

## Known failure modes

- DOI not found in Unpaywall or OpenAlex — no open-access record returned
- Malformed or non-existent DOI — error or empty result
- Paper exists but no open-access copy is available — returns false for OA status
- Rate limiting or upstream provider unavailability causing request failure

## How this service works

Locate a free open-access PDF for a DOI. Returns whether an open-access copy exists and the best PDF link with its license, version and host type, from Unpaywall and OpenAlex. A cheap, focused open-access locator.

## Output

Returns whether an open-access copy exists for the given DOI, the best available PDF URL, the license (e.g. CC-BY), the version (e.g. acceptedVersion, publishedVersion), and the host type (e.g. repository, publisher) sourced from Unpaywall and OpenAlex.

## 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",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [],
     "properties": {
      "id": {
       "type": "string",
       "description": "A DOI (alias for doi)"
      },
      "doi": {
       "type": "string",
       "description": "DOI, with or without a doi.org prefix"
      }
     }
    }
   },
   "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/open-access-pdf-locator-for-doi-9491ea93/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.agentstools.dev](https://www.zero.xyz/host/api.agentstools.dev/llms.txt)