Research Doi

{
  "exampleTruncated": true,
  "fixedSubject": "10.1038/nphys1170",
  "report": {
    "authors": [
      "Markus Aspelmeyer"
    ],
    "citation": "Markus Aspelmeyer. (2009). Measured measurement. Nature Physics. https://doi.org/10.1038/nphys1170",
    "citedByCount": 11,
    "doi": "10.1038/nphys1170",
    "publication": "Nature Physics",
    "publisher": "Springer Science and Business Media LLC",
    "referenceCount": 10,
    "title": "Measured measurement",
    "type": "journal-article",
    "url": "https://doi.org/10.1038/nphys1170",
    "year": 2009
  },
  "retrievedAt": "2026-09-18T13:57:05.553Z",
  "sample": true,
  "service": "doi",
  "source": {
    "name": "Crossref",
    "url": "https://api.crossref.org/works/10.1038%2Fnphys1170"
  },
  "subject": "10.1038/nphys1170"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://saylorinnovations.com/api/research/doi?doi=10.1038%2Fnphys1170'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://saylorinnovations.com/api/research/doi?doi=10.1038%2Fnphys1170' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.01 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.01" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.01 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fsaylorinnovations.com%2Fapi%2Fresearch%2Fdoi
const res = await pay("https://saylorinnovations.com/api/research/doi?doi=10.1038%2Fnphys1170");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.01 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.01"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://saylorinnovations.com/api/research/doi?doi=10.1038%2Fnphys1170")
    print(res.status_code, res.text)