How to Build a LangChain Web Scraper Tool That Pays per Page

Give a LangChain agent two tools: web_search (up to 10 results, $0.008 per call) and read_url (page to markdown, $0.003 per call). Your code pays each call over x402 in USDC on Base, so there is no API key to manage and failed calls cost nothing.

Steps

1. Install. pip install "x402[requests,evm]" langchain-core. The x402 client wraps requests and pays HTTP 402 responses.
2. Fund a wallet on Base. Hold a little USDC on Base and export the private key as AGENT_KEY. Set a spending cap of your own: the client pays every 402 it receives.
3. Define the tools. Wrap /v1/search and /v1/scrape/lite with the @tool decorator so the model sees a name, a description and typed arguments.
4. Bind them to your agent. Pass [web_search, read_url] to your chat model's bind_tools or to your agent constructor.

Code

# 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 import ExactEvmScheme

client = x402ClientSync()
client.register("eip155:8453", ExactEvmScheme(signer=EthAccountSigner(Account.from_key(os.environ["AGENT_KEY"]))))
session = x402_requests(client)
session.headers["User-Agent"] = "my-agent/1.0"

from langchain_core.tools import tool

@tool
def web_search(query: str, limit: int = 5) -> list:
    """Search the web. Returns up to 10 results with rank, title, url and snippet."""
    r = session.post("https://api.switch402.com/v1/search", json={"q": query, "limit": limit})  # $0.008
    r.raise_for_status()
    return r.json()["results"]

@tool
def read_url(url: str) -> str:
    """Read a public web page and return it as markdown."""
    r = session.post("https://api.switch402.com/v1/scrape/lite", json={"url": url})  # $0.003
    if r.status_code != 200:
        return f"Could not read {url} (HTTP {r.status_code}, not charged)"
    return r.json()["markdown"][:20000]

tools = [web_search, read_url]
# llm_with_tools = your_chat_model.bind_tools(tools)

curl -s 'https://api.switch402.com/v1/quote?url=https://example.com&tier=lite' -H 'User-Agent: my-agent/1.0'

You pay only for the pages you actually fetch: $0.008 per standard page on /v1/scrape, $0.003 per lite call on /v1/scrape/lite, in USDC on Base and charged only on success. No subscription or unused credits; optional prepaid packs and a $10 monthly plan.