research by fourzerotwo

DOI lookup

Title, authors, journal, dates, references count and licence for a DOI.

DOI lookup Free

Title, authors, journal, dates, references count and licence for a DOI.

cost: Free then $0.002 / call
MCP tool: crossref__doi
method: GET

Free up to 50 calls a day over MCP (500 with a free key), then $0.002 per call by card credit or USDC. Free key · Pay by card

GET https://fourzerotwo.si/v1/crossref/doi

Param	Type	Description
doi	string	DOI

# free: send a free key from https://fourzerotwo.si/free
curl -H "X-API-Key: fzt_…" "https://fourzerotwo.si/v1/crossref/doi?doi=10.1038%2Fnature14539"

# no key: returns 402 with the price, for x402 agents
curl -i "https://fourzerotwo.si/v1/crossref/doi?doi=10.1038%2Fnature14539"

by fourzerotwo

Report this endpoint

Use it from an AI agent (MCP)

Add the server once, then ask for this data in plain English. The agent finds the endpoint with search_apis and runs it with call_api.

{
  "mcpServers": {
    "fourzerotwo": { "type": "http", "url": "https://fourzerotwo.si/mcp" }
  }
}

# the call the agent makes
call_api {"tool": "crossref__doi", "arguments": {"doi":"10.1038/nature14539"}}

DOI lookup

DOI lookup Free

Use it from an AI agent (MCP)

More from Crossref DOI Metadata