paper.doi-lookup

Resolve a DOI to authoritative bibliographic metadata via Crossref. Accepts bare DOI (10.1038/nature12373) or full DOI URL (https://doi.org/10.1038/nature12373). Returns work type, title, container (journal/conference), publisher, issued/published dates, abstract, authors (with ORCID + affiliations), page range, volume/issue, ISBN + ISSN lists, canonical URL, reference + citation counts, license blocks, and subject classifications. ~160M works in Crossref. Best authoritative DOI → bibliographic resolver. Metadata is CC0.

price

$0.0012 USDC per call

method

GET/api/paper/doi-lookup

payment

x402 v2 · USDC on Base (EIP-3009) or Solana (SPL transfer)

auth

None. Sign the payment, retry with PAYMENT-SIGNATURE.

tier

Tier 0 — no paid upstream

Parameters

Name	Type	Description
`doi`required	string	min 7 chars · max 300 chars

Code samples

cURLbash

# 1. Probe with no auth → 402 envelope with PaymentRequirements
curl -sS 'https://2s.io/api/paper/doi-lookup?doi=xxxxxxx'

# 2. Sign + retry with PAYMENT-SIGNATURE:
curl -sS 'https://2s.io/api/paper/doi-lookup?doi=xxxxxxx' \
  -H 'PAYMENT-SIGNATURE: <base64-json-payload>'

# Or use the canonical runner (handles probe → sign → retry):
#   EVM_PRIVATE_KEY=0x... node --env-file=.env.local \
#     --experimental-strip-types scripts/x402-pay.ts \
#     'https://2s.io/api/paper/doi-lookup?doi=xxxxxxx'

TypeScript / Node — @2sio/sdktypescript

import { TwoS } from '@2sio/sdk'

const client = new TwoS({
  privateKey: process.env.EVM_PRIVATE_KEY as `0x${string}`,
})

const result = await client.paper.doiLookup({
  "doi": "xxxxxxx"
})

console.log('endpoint:', result.endpoint)
console.log('cost:', result.costUsd, 'USDC')
console.log('tx:', result.settlement?.txHash)
console.log('data:', result.data)

Python — 2siopython

import os
from twosio import TwoS

client = TwoS(private_key=os.environ["EVM_PRIVATE_KEY"])

result = client.paper.doi_lookup(doi="xxxxxxx")

print("endpoint:", result.endpoint)
print("cost:", result.cost_usd, "USDC")
print("tx:", (result.settlement or {}).get("tx_hash"))
print("data:", result.data)

MCP — Claude Desktop / AgentKit / any MCP hostjson

// 1. Add @2sio/mcp to your MCP host config (Claude Desktop example below).
//    EVM_PRIVATE_KEY funds x402 payments per call.

// claude_desktop_config.json
{
  "mcpServers": {
    "2sio": {
      "command": "npx",
      "args": ["-y", "@2sio/mcp"],
      "env": { "EVM_PRIVATE_KEY": "0x..." }
    }
  }
}

// 2. Once the server is running, agents call this tool via standard MCP:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "paper.doi-lookup",
    "arguments": {
      "doi": "xxxxxxx"
    }
  }
}

Response

Field	Type	Description
`doi`	string
`type`	string
`title`	string
`containerTitle`	string
`publisher`	string
`issued`	string
`publishedPrint`	string
`publishedOnline`	string
`abstract`	string
`authors`	array
`pageRange`	string
`volume`	string
`issue`	string
`isbn`	array
`issn`	array
`url`	string
`referenceCount`	integer
`isReferencedByCount`	integer
`license`	array
`subjects`	array
`source`	object

Example response datajson

{
  "doi": "example",
  "type": "example",
  "title": "example",
  "containerTitle": "example",
  "publisher": "example",
  "issued": "example",
  "publishedPrint": "example",
  "publishedOnline": "example",
  "abstract": "example",
  "authors": [
    {
      "given": "example",
      "family": "example",
      "orcid": "example",
      "affiliation": [
        "example"
      ]
    }
  ],
  "pageRange": "example",
  "volume": "example",
  "issue": "example",
  "isbn": [
    "example"
  ],
  "issn": [
    "example"
  ],
  "url": "example",
  "referenceCount": 1,
  "isReferencedByCount": 1,
  "license": [
    {
      "url": "example",
      "contentVersion": "example"
    }
  ],
  "subjects": [
    "example"
  ],
  "source": {
    "provider": "example",
    "url": "https://example.com",
    "license": "example"
  }
}

Discovery

/api/directory — full catalog of every endpoint
/openapi.json — OpenAPI 3.1 spec (per-op x-payment-info, x402Payment security)
/.well-known/x402 — machine-readable service descriptor for x402-aware crawlers
/.well-known/mcp/server-card.json — MCP SEP-1649 server card
/llms.txt — plain-text manifest for LLM ingestion

2s.io is x402-native. Every call is paid per-request from a USDC-funded EVM wallet on Base — no signup, no API keys, no monthly fees. Source code: github.com/2s-io/sdk.