A LangChain tool that pays for its own call.

# tools/convert_currency.py
# pip install "x402[requests,evm]" langchain-core

import os

from eth_account import Account
from langchain_core.tools import tool
from x402 import x402ClientSync
from x402.http.clients.requests import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

account = Account.from_key(os.environ["WALLET_PRIVATE_KEY"])

# x402ClientSync is the payment client, not an HTTP client. Register a signer
# against it, then hand it to x402_requests to get a requests.Session that
# answers the 402 on its own.
payments = x402ClientSync()
register_exact_evm_client(payments, EthAccountSigner(account))

session = x402_requests(payments)


@tool(parse_docstring=True)
def convert_currency(from_code: str, to_code: str, amount: float) -> dict:
    """Convert an amount between two currencies using live FX rates.

    Args:
        from_code: ISO currency code to convert from, e.g. EUR.
        to_code: ISO currency code to convert to, e.g. USD.
        amount: Amount to convert.
    """
    response = session.get(
        "https://gateway.apiosk.com/v1/fx/convert",
        params={"from": from_code, "to": to_code, "amount": amount},
        timeout=30,
    )
    response.raise_for_status()
    return response.json()

# tools/verify_email.py

from langchain_core.tools import tool

# One payment-aware session for every tool. The wallet is built once, in
# tools/convert_currency.py.
from tools.convert_currency import session


@tool(parse_docstring=True)
def verify_email(email: str) -> dict:
    """Check whether an email address is deliverable.

    Args:
        email: The address to check, e.g. ada@example.com.
    """
    response = session.get(
        "https://gateway.apiosk.com/v1/email/verify",
        params={"email": email},
        timeout=30,
    )
    response.raise_for_status()
    return response.json()

# agent.py
# pip install langchain langchain-anthropic

from langchain.agents import create_agent

from tools.convert_currency import convert_currency
from tools.verify_email import verify_email

agent = create_agent(
    "anthropic:claude-opus-5",
    tools=[convert_currency, verify_email],
)

result = agent.invoke(
    {"messages": [{"role": "user", "content": "What is 250 EUR in USD right now?"}]}
)

print(result["messages"][-1].content)