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

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" 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