crossref is a scholarly infrastructure organization that provides 
persistent identifiers (dois) for scholarly content and metadata.
it's one of the largest citation databases covering millions of 
academic papers, journals, books, and other scholarly content.

args:
    query: search query string (e.g., 'machine learning', 'climate change').
    max_results: maximum number of papers to return (default: 10, max: 1000).
    **kwargs: additional search parameters:
        - filter: crossref filter string (e.g., 'has-full-text:true,from-pub-date:2020')
        - sort: sort field ('relevance', 'published', 'updated', 'deposited', etc.)
        - order: sort order ('asc' or 'desc')
returns:
    list of paper metadata in dictionary format.
    
examples:
    # basic search
    search_crossref("deep learning", 20)
    
    # search with filters
    search_crossref("climate change", 10, filter="from-pub-date:2020,has-full-text:true")
    
    # search sorted by publication date
    search_crossref("neural networks", 15, sort="published", order="desc")
. This is part of the Paper Search provider on xpay✦.

{
  "mcpServers": {
    "xpay": {
      "url": "https://mcp.xpay.sh/mcp?key=YOUR_API_KEY"
    }
  }
}

claude mcp add --transport http xpay "https://mcp.xpay.sh/mcp?key=YOUR_API_KEY"