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Alex Spinov
Alex Spinov

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Crossref API: Search 150M+ Academic Articles for Free (No API Key)

#api #python #research #tutorial

Crossref indexes 150 million+ academic articles with DOIs, citations, and metadata. Their API is completely free with no key required.

curl "https://api.crossref.org/works?query=machine+learning&rows=3"
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That returns structured JSON with title, authors, DOI, citations, journal, and publication date. No authentication needed.

Python Client 

import requests

def search_crossref(query, limit=10):
    url = "https://api.crossref.org/works"
    params = {
        "query": query,
        "rows": limit,
        "sort": "relevance"
    }
    # Polite pool: add your email for faster responses
    headers = {"User-Agent": "MyApp/1.0 (mailto:your@email.com)"}

    response = requests.get(url, params=params, headers=headers)
    data = response.json()

    for item in data["message"]["items"]:
        title = item.get("title", ["No title"])[0]
        doi = item.get("DOI", "no DOI")
        cited = item.get("is-referenced-by-count", 0)
        year = item.get("published-print", {}).get("date-parts", [[None]])[0][0]
        print(f"[{year}] {title}")
        print(f"  DOI: {doi} | Cited by: {cited}")
        print()

search_crossref("CRISPR gene editing", limit=5)
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What You Can Query

Endpoint Returns Example
/works Articles, papers ?query=quantum+computing
/journals Journal metadata ?query=Nature
/funders Funding organizations ?query=NIH
/members Publishers ?query=Elsevier

Advanced Filters 

# Papers from 2024, cited 50+ times, about AI
params = {
    "query": "artificial intelligence",
    "filter": "from-pub-date:2024,has-references:true",
    "sort": "is-referenced-by-count",
    "order": "desc",
    "rows": 25
}
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Pro Tips

  1. Add your email in User-Agent header — you get moved to the "polite pool" with faster responses
  2. Use cursor-based pagination for large result sets (not offset)
  3. Filter by DOI prefix to search specific publishers
  4. Combine with OpenAlex for richer metadata

Use Cases

  • Literature reviews — find most-cited papers in any field
  • Citation analysis — track how papers influence each other
  • Journal discovery — find where to publish
  • Research trends — volume of papers by topic over time
  • Data journalism — back claims with real research data

Free Research API Stack

API Papers Best For
OpenAlex 250M+ Broadest coverage
Crossref 150M+ DOIs and citations
Semantic Scholar 200M+ AI/CS papers
arXiv 2M+ Preprints
PubMed 36M+ Medical research

All free. All keyless. Use them together for comprehensive research.

More Free APIs

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