Citation graph for a scholarly work via OpenAlex. Pass id as a DOI (10.xxxx/…, doi.org URL) or an OpenAlex work id (W…). Returns the work's total citation count + reference count, and a paginated list of either the works that CITE it (view=citing, default — sort=recent for newest-first or sort=citations for most-cited-first) or the works it REFERENCES (view=referenced). Each listed work gives DOI, title, year, venue, authors, and its own citation count. Fresh citation data lands after any training cutoff. Complements papers.search (finding papers) with graph traversal (following citations).
/api/papers/citationsPAYMENT-SIGNATURE.The citations API is a pay-per-call papers endpoint built for AI agents and autonomous software. Citation graph for a scholarly work via OpenAlex.
There is no signup and no API key. An agent (or any HTTP client) hits the endpoint, receives an x402 "402 Payment Required" challenge, signs a sub-cent USDC payment on Base or Solana, and retries — the data comes back on the paid request. That makes it a drop-in citations data source for an agent tool-use loop, an MCP host, or a backend that needs papers data on demand without onboarding to yet another vendor portal.
| Name | Type | Description |
|---|---|---|
idrequired | string | DOI or OpenAlex work id. min 4 chars · max 500 chars |
view | string | one of: citing | referenced |
page | integer | min 1 · max 200 |
limit | integer | min 1 · max 50 |
sort | string | one of: recent | citations |
# 1. Probe with no auth → 402 envelope with PaymentRequirements curl -sS 'https://2s.io/api/papers/citations?id=xxxx&view=citing&page=1&limit=10&sort=recent' # 2. Sign + retry with PAYMENT-SIGNATURE: curl -sS 'https://2s.io/api/papers/citations?id=xxxx&view=citing&page=1&limit=10&sort=recent' \ -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/papers/citations?id=xxxx&view=citing&page=1&limit=10&sort=recent'
import { TwoS } from '@2sio/sdk'
const client = new TwoS({
privateKey: process.env.EVM_PRIVATE_KEY as `0x${string}`,
})
const result = await client.papers.citations({
"id": "xxxx",
"view": "citing",
"page": 1,
"limit": 10,
"sort": "recent"
})
console.log('endpoint:', result.endpoint)
console.log('cost:', result.costUsd, 'USDC')
console.log('tx:', result.settlement?.txHash)
console.log('data:', result.data)import os
from twosio import TwoS
client = TwoS(private_key=os.environ["EVM_PRIVATE_KEY"])
result = client.papers.citations(id="xxxx", view="citing", page=1, limit=10, sort="recent")
print("endpoint:", result.endpoint)
print("cost:", result.cost_usd, "USDC")
print("tx:", (result.settlement or {}).get("tx_hash"))
print("data:", result.data)// 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": "papers.citations",
"arguments": {
"id": "xxxx",
"view": "citing",
"page": 1,
"limit": 10,
"sort": "recent"
}
}
}| Field | Type | Description |
|---|---|---|
ok | boolean | one of: true |
items | array | |
total | integer | Total matching rows upstream; null when unknown. |
source | object | |
page | object | |
meta | object |
{
"ok": true,
"items": [
{
"id": "example",
"doi": "example",
"title": "example",
"year": 1,
"publishedAt": "example",
"citedByCount": 1,
"authors": [
"example"
],
"authorCount": 1,
"venue": "example",
"url": "example"
}
],
"total": 1,
"source": {
"provider": "example",
"url": "example",
"license": "example"
},
"page": {
"number": 1,
"size": 1,
"pages": 1
},
"meta": {
"view": "example",
"work": {
"id": "example",
"doi": "example",
"title": "example",
"year": 1,
"citedByCount": 1,
"referencedCount": 1
}
}
}