OpenAlex & CrossRef API Guide

Overview

OpenAlex is a free, open catalog of the global research system, indexing over 250 million academic works across all fields of science. It provides structured access to papers, authors, institutions, concepts, and citation networks. OpenAlex is the successor to Microsoft Academic Graph and is maintained by OurResearch (the team behind Unpaywall).

CrossRef is the official DOI registration agency for scholarly content, providing metadata for over 150 million DOIs across all publishers and disciplines. Together, OpenAlex and CrossRef provide comprehensive coverage for academic search, citation analysis, and bibliometric research.

Both APIs are free to use without authentication. OpenAlex requests a polite User-Agent header; CrossRef requests a User-Agent with contact email for access to the polite pool (faster rate limits).

Authentication

No authentication is required for either API.

OpenAlex: Include a User-Agent header for polite access:

User-Agent: ResearchPlugins/1.0 (https://wentor.ai)

CrossRef: Include a User-Agent header with contact email for polite pool:

User-Agent: ResearchPlugins/1.0 (https://wentor.ai; mailto:dev@wentor.ai)

Core Endpoints

OpenAlex: Search Works

• URL: GET https://api.openalex.org/works
• Parameters:

  Param	Type	Required	Description
  search	string	No	Full-text search query
  filter	string	No	Filter expression (e.g., from_publication_date:2024-01-01)
  sort	string	No	Sort field (e.g., cited_by_count:desc, publication_date:desc)
  per_page	integer	No	Results per page (default: 25, max: 200)
  page	integer	No	Page number (default: 1)

• Example:

  curl "https://api.openalex.org/works?search=attention+is+all+you+need&per_page=5"
  

• Response: JSON with meta (count, page info) and results array containing work objects.

OpenAlex: Get Work Details

• URL: GET https://api.openalex.org/works/{id}
• Parameters:

  Param	Type	Required	Description
  id	string	Yes	OpenAlex ID (e.g., W2741809807), DOI URL, or other identifier

• Example:

  curl "https://api.openalex.org/works/W2741809807"
  

• Response: JSON with full work metadata including id, title, abstract_inverted_index, publication_year, cited_by_count, authorships, concepts, referenced_works.

OpenAlex: Search Authors

• URL: GET https://api.openalex.org/authors
• Parameters:

  Param	Type	Required	Description
  search	string	No	Author name search
  filter	string	No	Filter expression
  per_page	integer	No	Results per page (max: 200)

• Example:

  curl "https://api.openalex.org/authors?search=Yoshua+Bengio&per_page=5"
  

• Response: JSON with author profiles including works_count, cited_by_count, summary_stats.h_index, affiliations.

CrossRef: Resolve DOI

• URL: GET https://api.crossref.org/works/{doi}
• Parameters:

  Param	Type	Required	Description
  doi	string	Yes	DOI to resolve (e.g., 10.1038/nature12373)

• Example:

  curl "https://api.crossref.org/works/10.18653/v1/N19-1423"
  

• Response: JSON with full bibliographic metadata including title, authors, journal, dates, references count, and citation count.

Rate Limits

OpenAlex: No strict rate limit, but use polite User-Agent header. Recommended: max 10 requests per second. The API returns HTTP 429 when limits are exceeded.

CrossRef: Without polite pool: ~50 requests per second. With polite pool (contact email in User-Agent): higher limits. The API returns HTTP 429 when limits are exceeded.

Common Patterns

Build a Citation Network

Retrieve a paper and find all works that cite it:

# Get paper details
curl "https://api.openalex.org/works/W2741809807"

# Get works citing this paper, sorted by citation count
curl "https://api.openalex.org/works?filter=cites:W2741809807&sort=cited_by_count:desc&per_page=20"

Find Influential Papers on a Topic

Search for highly cited works on a topic:

curl "https://api.openalex.org/works?search=graph+neural+networks&sort=cited_by_count:desc&per_page=20"

Batch Paper Lookup via CrossRef

Search CrossRef for papers matching a query, sorted by citation count:

curl "https://api.crossref.org/works?query=graph+neural+networks&sort=is-referenced-by-count&order=desc&rows=20"

References

• OpenAlex documentation: https://docs.openalex.org/
• CrossRef API documentation: https://api.crossref.org/swagger-ui/index.html
• OpenAlex source: https://github.com/ourresearch/openalex-guts