# Unpaywall API: Get free version of a paper > Finds 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, the copy links are null. Unofficial. Not affiliated with or endorsed by Unpaywall. - Page: https://fous.com/methods/unpaywall.org/get-free-version - Method: `unpaywall.org/get_free_version`, version 1 - Website: unpaywall.org - Returns: title, journal, year, DOI, best free link, landing page, host, licence, version, other free copies - Effect: read (it gets data and changes nothing) - Sign-in: none needed - Cost: 1 credit per completed run (1ยข with pay as you go); failed runs are free - Verified: Nov 2, 2026 ## Inputs | Field | Type | Required | In the run below | 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 | | Optional author name to distinguish papers with similar titles, for example Edmond Awad. Default "". | ## Output From a run on Oct 23, 2026. Its input: ```json { "paper": "10.1038/35057062" } ``` Its 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" } ] } ``` ## Run it From code, with a Fous API key in `FOUS_API_KEY`; the answer's `data` holds the output: ```bash curl https://api.fous.com/v1/runs \ -H "Authorization: Bearer $FOUS_API_KEY" \ -H "Content-Type: application/json" \ -d '{"method":"unpaywall.org/get_free_version","input":{"paper":"10.1038/35057062"}}' ``` From an AI agent connected to the Fous MCP server: its `run` with the same method and input. To connect one, give it `set up https://fous.com/SKILL.md`. ## Ask your agent - Find a free legal copy of the paper The Moral Machine experiment - Is there an open access version of DOI 10.1038/s41586-018-0637-6? - Get the free full text for the 2019 paper on transformer attention by Vaswani - Where can I read the paper Deep residual learning for image recognition for free? - On unpaywall.org, look up a legal free copy of the article titled Attention Is All You Need ## 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." }, "author": { "type": "string", "default": "", "description": "Optional author name to distinguish papers with similar titles, for example Edmond Awad." } } } ``` ## Output schema ```json { "type": "object", "required": [ "title", "journal", "year", "doi", "free_to_read", "best_free_link", "landing_page", "host", "licence", "version", "other_free_copies" ], "properties": { "doi": { "type": "string" }, "host": { "type": [ "string", "null" ] }, "year": { "type": [ "integer", "null" ] }, "title": { "type": "string" }, "journal": { "type": [ "string", "null" ] }, "licence": { "type": [ "string", "null" ] }, "version": { "type": [ "string", "null" ] }, "free_to_read": { "enum": [ "yes", "no" ], "type": "string" }, "landing_page": { "type": [ "string", "null" ] }, "best_free_link": { "type": [ "string", "null" ] }, "other_free_copies": { "type": "array", "items": { "type": "object", "required": [ "link", "host", "landing_page" ], "properties": { "host": { "type": "string" }, "link": { "type": "string" }, "landing_page": { "type": [ "string", "null" ] } }, "additionalProperties": false } } }, "additionalProperties": false } ``` ## See more - [Semantic Scholar API: Get paper details](https://fous.com/methods/semanticscholar.org/get-paper.md): Finds a paper on Semantic Scholar by title, DOI or Semantic Scholar link and returns its abstract, one-sentence summary, authors, publication details, citation counts and a free PDF link when there is one. - [arXiv API: Get paper](https://fous.com/methods/arxiv.org/get-paper.md): Gets an arXiv paper's title, authors, abstract, subjects, submission dates and publication details from its exact title, arXiv link or number. - [OpenAlex API: Search scholarly papers](https://fous.com/methods/openalex.org/search-papers.md): Searches OpenAlex scholarly works by topic, with optional institution, publication-year and open-access filters, ranked by relevance, citations or newest date. - [Semantic Scholar API: Search papers](https://fous.com/methods/semanticscholar.org/search-papers.md): Searches Semantic Scholar for research papers in relevance order, with field of study, year range and open-access filters, returning AI one-sentence summaries, citations and free PDF links when available. - [NIH API: Get PubMed article](https://fous.com/methods/pubmed.ncbi.nlm.nih.gov/get-article.md): Gets the full PubMed abstract and publication details for one article by title, PubMed link, or PubMed number (PMID). A title is searched in PubMed titles first and must closely match a found article. Some articles have no abstract or free full text. - [arXiv API: Search papers](https://fous.com/methods/arxiv.org/search-papers.md): Finds arXiv preprints by topic or title words, with optional author, subject, submission date range and sorting. Returns up to 100 papers with abstracts, subjects, dates and links. - [Crossref API: Get citation](https://fous.com/methods/crossref.org/get-citation.md): Gets a formatted citation and publication details for the best-matching Crossref work by title or DOI. Optional author and year help choose among similar works; citations reflect the metadata deposited with Crossref. - [OverDrive API: Check library availability](https://fous.com/methods/overdrive.com/check-library-availability.md): Finds ebook and audiobook editions a public library owns on OverDrive, with copies, holds and estimated wait when unavailable.