# Unpaywall API

> Unpaywall returns open-access paper links and copy details as a workflow and API.

Unpaywall finds a legal free copy of a paper using its title or DOI, with an optional author name to distinguish similar titles. Get free version returns the best available link and other copies; if no free copy is indexed, copy links are null.

- Page: https://fous.com/workflows/unpaywall
- Handle: `@unpaywall`
- Category: [Science](https://fous.com/workflows/category/science)
- Source website: https://unpaywall.org
- Last verified: Sep 29, 2026
- Fous is not affiliated with Unpaywall.

## Methods

### Get free version

Operation `get_free_version`, version 1. 1 credit per call.

Find a legal free copy of a paper by title or DOI, with its best available link and other copies. If no free copy is indexed, copy links are null.

**Input**

| Field | Type | Required | Example | Description |
|---|---|---|---|---|
| `paper` | string | yes | `"10.1038/35057062"` | Paper title or DOI, for example The Moral Machine experiment or 10.1038/s41586-018-0637-6. |
| `author` | string | no | `"Edmond Awad"` | Optional author name to distinguish papers with similar titles, for example Edmond Awad. |

**Input schema**

```json
{
  "type": "object",
  "required": [
    "paper"
  ],
  "properties": {
    "paper": {
      "type": "string",
      "description": "Paper title or DOI, for example The Moral Machine experiment or 10.1038/s41586-018-0637-6.",
      "examples": [
        "10.1038/35057062",
        "The Moral Machine experiment",
        "10.1038/nature01092"
      ]
    },
    "author": {
      "type": "string",
      "default": "",
      "description": "Optional author name to distinguish papers with similar titles, for example Edmond Awad.",
      "examples": [
        "Edmond Awad"
      ]
    }
  },
  "additionalProperties": false,
  "examples": [
    {
      "paper": "10.1038/35057062"
    },
    {
      "paper": "The Moral Machine experiment",
      "author": "Edmond Awad"
    },
    {
      "paper": "10.1038/nature01092"
    }
  ]
}
```

**Output**

| Field | Type | Example | Description |
|---|---|---|---|
| `doi` | string | `"10.1038/35057062"` |  |
| `host` | string or null | `"Springer Science and Business Media LLC"` |  |
| `year` | integer or null | `2001` |  |
| `title` | string | `"Initial sequencing and analysis of the human genome"` |  |
| `journal` | string or null | `"Nature"` |  |
| `licence` | string or null | `"Public domain"` |  |
| `version` | string or null | `"published"` |  |
| `free_to_read` | string | `"yes"` |  |
| `landing_page` | string or null | `"https://doi.org/10.1038/35057062"` |  |
| `best_free_link` | string or null | `"https://www.nature.com/articles/35057062.pdf"` |  |
| `other_free_copies` | array |  |  |
| `other_free_copies[].host` | string | `"University of Michigan"` |  |
| `other_free_copies[].link` | string | `"https://hdl.handle.net/2027.42/62798"` |  |
| `other_free_copies[].landing_page` | string or null | `"https://hdl.handle.net/2027.42/62798"` |  |

**Example input**

```json
{
  "paper": "10.1038/35057062"
}
```

**Example output**

```json
{
  "doi": "10.1038/35057062",
  "host": "Springer Science and Business Media LLC",
  "year": 2001,
  "title": "Initial sequencing and analysis of the human genome",
  "journal": "Nature",
  "licence": "Public domain",
  "version": "published",
  "free_to_read": "yes",
  "landing_page": "https://doi.org/10.1038/35057062",
  "best_free_link": "https://www.nature.com/articles/35057062.pdf",
  "other_free_copies": [
    {
      "host": "University of Michigan",
      "link": "https://hdl.handle.net/2027.42/62798",
      "landing_page": "https://hdl.handle.net/2027.42/62798"
    }
  ]
}
```

## Quick start

Call the API with a Fous API key (`FOUS_API_KEY`). To create one, turn on Developer mode in Fous Studio, then open Keys & connections → API keys (https://app.fous.com/keys).

```bash
# First set your key: export FOUS_API_KEY='YOUR_FOUS_API_KEY'
: "${FOUS_API_KEY:?Set FOUS_API_KEY before running this example}"

curl 'https://api.fous.com/v1/query' \
  --fail-with-body --silent --show-error --max-time 120 \
  -H "Authorization: Bearer $FOUS_API_KEY" \
  -H 'Content-Type: application/json' \
  --data-raw '{
  "api": "@unpaywall",
  "visibility": "public",
  "operation": "get_free_version",
  "version": 1,
  "input": {
    "paper": "10.1038/35057062"
  },
  "response": {
    "format": "json"
  }
}'
```

```python
# Save as fous.py and run with python3 fous.py. No packages needed.
# First set your key: export FOUS_API_KEY='YOUR_FOUS_API_KEY'
import json
import os
import urllib.error
import urllib.request

api_key = os.environ.get("FOUS_API_KEY")
if not api_key:
    raise RuntimeError("Set FOUS_API_KEY before running this example")

body = json.loads("{\n  \"api\": \"@unpaywall\",\n  \"visibility\": \"public\",\n  \"operation\": \"get_free_version\",\n  \"version\": 1,\n  \"input\": {\n    \"paper\": \"10.1038/35057062\"\n  },\n  \"response\": {\n    \"format\": \"json\"\n  }\n}")
request = urllib.request.Request(
    "https://api.fous.com/v1/query",
    data=json.dumps(body).encode("utf-8"),
    headers={
        "Authorization": f"Bearer {api_key}",
        "Content-Type": "application/json",
    },
    method="POST",
)
try:
    with urllib.request.urlopen(request, timeout=120) as response:
        result = json.load(response)
except urllib.error.HTTPError as error:
    raise RuntimeError(f"HTTP {error.code}: {error.read().decode('utf-8', errors='replace')}") from error
if result.get("success") is False:
    raise RuntimeError(result.get("error", {}).get("message", "Request failed"))
print(json.dumps(result["data"]["output"], indent=2))
```

```typescript
// Save as fous.mts and run with npx tsx fous.mts.
// First set your key: export FOUS_API_KEY='YOUR_FOUS_API_KEY'
const apiKey = process.env.FOUS_API_KEY;
if (!apiKey) throw new Error("Set FOUS_API_KEY before running this example");

const response = await fetch("https://api.fous.com/v1/query", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${apiKey}`,
    "Content-Type": "application/json",
  },
  signal: AbortSignal.timeout(120_000),
  body: JSON.stringify({
  "api": "@unpaywall",
  "visibility": "public",
  "operation": "get_free_version",
  "version": 1,
  "input": {
    "paper": "10.1038/35057062"
  },
  "response": {
    "format": "json"
  }
}),
});
type ApiResult = { success: boolean; data?: { output: unknown }; error?: { message: string } };
const result: ApiResult = await response.json();
if (!response.ok || result.success === false) {
  throw new Error(result.error?.message ?? `HTTP ${response.status}`);
}
if (!result.data) throw new Error("Missing API response data");
console.log(result.data.output);
```

Or describe the data in plain language: send `{"api":"@unpaywall","prompt":"Describe the data you need, with every detail"}` to the same URL. Fous fills in the input, runs the method that fits and returns only the fields you asked for; `data.route.calls[].request` is the exact call it made. Routing is free; the run costs the same.

## Use cases

- Find free versions of papers by title or DOI
- Distinguish papers with similar titles using an author name
- Compare available copies by host and landing page
- Check a paper’s journal, year, licence, and version

## FAQ

### Is Fous affiliated with Unpaywall?

No. Fous is not affiliated with Unpaywall. This workflow reads the public unpaywall.org website and returns its data.

### How much does it cost?

Each run costs 1 credit. With pay-as-you-go, a credit costs 1¢; monthly plans cost less per credit.

### Do I need a Unpaywall account?

No. You only need a Fous account.

### How current is the data?

Fous gets the data from unpaywall.org when you run it; repeating the same request within a day may return the saved result. Fous checks this workflow automatically; it last passed a check on Sep 29, 2026.

### Can I find a free copy by paper title?

Yes. Get free version accepts a paper title or DOI and returns the best available link when a free copy is indexed.

### Can I find other copies of a paper?

Get free version returns other available copies, including their host, link, and landing page.

### What if no free copy is indexed?

Get free version returns null copy links when no free copy is indexed.

## Related

- [Semantic Scholar API](https://fous.com/workflows/semantic-scholar.md): Semantic Scholar returns paper and citation search, paper abstracts, summaries, authors and influence, plus author metrics and up to 10 top-cited papers; dates, summaries, PDFs and affiliation matches may be unavailable.
- [OpenAlex API](https://fous.com/workflows/openalex.md): OpenAlex is an open catalog of scholarly research and connections, offering ranked papers and institution research summaries with annual output, leading topics, and coauthors.
- [arXiv API](https://fous.com/workflows/arxiv.md): arXiv returns up to 100 matching research preprints or individual paper details, and newly announced subject papers in announcement order; announcement dates may differ from today, and replacements are excluded.
- [Crossref API](https://fous.com/workflows/crossref.md): Find scholarly works and format citations from their registered metadata.
- [Google Scholar API](https://fous.com/workflows/google-scholar.md): Google Scholar provides papers, citing papers, ready-made citations and researcher profiles with metrics and up to 20 top-cited papers; public access may be temporarily limited.
- [PubMed API](https://fous.com/workflows/pubmed.md): PubMed searches medical and life-science articles by topic and retrieves one article’s abstract and publication details; abstracts and free full-text links may be unavailable.
- [AP News API](https://fous.com/workflows/ap-news.md): AP News provides reporting, up to 50 public-page headlines, searchable articles visible in its search, and full text when accessible.
- [OverDrive API](https://fous.com/workflows/overdrive.md): Find ebooks and audiobooks at public libraries.
- [All Science workflows](https://fous.com/workflows/category/science)