x402-langchain

March 14, 2026 · View on GitHub

LangChain tools for x402 Bazaar -- the AI agent API marketplace with native USDC payments.

Build autonomous AI agents that can search the web, scrape pages, check weather, get crypto prices, and more -- all paid automatically with USDC on Base, SKALE, or Polygon.

Installation

pip install x402-langchain

Quick Start

Free endpoint (no wallet needed)

from x402_langchain import X402Client

client = X402Client()
services = client.search("weather")
print(f"Found {len(services)} services")

Paid endpoint (automatic USDC payment)

from x402_langchain import X402Client

client = X402Client(
    private_key="0xYOUR_PRIVATE_KEY",
    chain="base",           # "base", "base-sepolia", "skale", or "polygon"
    max_budget_usdc=1.0,    # Safety cap
)

# Automatically pays 0.001 USDC and returns results
results = client.web_search("latest AI news")
print(results)

LangChain Agent

from langchain.agents import AgentExecutor, create_tool_calling_agent
from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI
from x402_langchain import X402BazaarTool

tools = [
    X402BazaarTool.search(),   # Free
    X402BazaarTool.web_search(private_key="0x..."),
    X402BazaarTool.weather(private_key="0x..."),
    X402BazaarTool.crypto(private_key="0x..."),
]

llm = ChatOpenAI(model="gpt-4o-mini")
prompt = ChatPromptTemplate.from_messages([
    ("system", "You are a helpful assistant with x402 Bazaar tools."),
    ("human", "{input}"),
    ("placeholder", "{agent_scratchpad}"),
])

agent = create_tool_calling_agent(llm, tools, prompt)
executor = AgentExecutor(agent=agent, tools=tools)
result = executor.invoke({"input": "What's the weather in Tokyo?"})

Available Tools

Tool	Endpoint	Cost	Description
`X402BazaarTool.search()`	`/api/services`	Free	Search the marketplace
`X402BazaarTool.web_search()`	`/api/search`	0.001 USDC	Web search (DuckDuckGo)
`X402BazaarTool.scrape()`	`/api/scrape`	0.002 USDC	Scrape any webpage to markdown
`X402BazaarTool.weather()`	`/api/weather`	0.001 USDC	Current weather data
`X402BazaarTool.crypto()`	`/api/crypto`	0.001 USDC	Cryptocurrency prices
`X402BazaarTool.image()`	`/api/image`	0.05 USDC	Image generation (DALL-E 3)

Configuration

Supported Chains

Chain	ID	Gas Cost
Base Mainnet	`base`	~$0.001
Base Sepolia (testnet)	`base-sepolia`	Free
SKALE on Base	`skale`	~$0.0007 (CREDITS)
Polygon Mainnet	`polygon`	~$0.001 (MATIC)

Budget Control

The max_budget_usdc parameter prevents runaway spending:

client = X402Client(
    private_key="0x...",
    max_budget_usdc=0.50,  # Will refuse payments after spending 0.50 USDC
)

Using the Client Directly

from x402_langchain import X402Client

client = X402Client(private_key="0x...", chain="base")

# Any x402 endpoint
result = client.call_api("/api/weather", params={"city": "London"})

# Check spending
print(f"Spent: {client.payment_handler.total_spent} USDC")
print(f"Remaining: {client.payment_handler.remaining_budget} USDC")
print(f"USDC Balance: {client.payment_handler.get_balance()} USDC")

How x402 Payment Works

Your agent calls a paid API endpoint
The server responds with HTTP 402 and payment details
x402-langchain automatically transfers USDC on-chain
The request is retried with the transaction hash
The server verifies the payment and returns data

All of this happens transparently -- your agent just calls the tool.

API Reference

X402Client

X402Client(
    private_key: str = None,    # Wallet private key (optional for free endpoints)
    base_url: str = "https://x402-api.onrender.com",
    chain: str = "base",
    max_budget_usdc: float = 1.0,
    timeout: int = 30,
)

Methods: search(), list_services(), call_api(), get_info(), web_search(), scrape(), weather(), crypto(), generate_image()

X402BazaarTool

X402BazaarTool(
    name: str,
    description: str,
    endpoint: str,
    param_name: str = "q",
    private_key: str = None,
    chain: str = "base",
    max_budget_usdc: float = 1.0,
)

Factory methods: search(), web_search(), scrape(), weather(), crypto(), image()

X402PaymentHandler

X402PaymentHandler(
    private_key: str,
    chain: str = "base",
    max_budget_usdc: float = 1.0,
)

Properties: address, chain, total_spent, remaining_budget Methods: pay(), get_balance()

Ecosystem

Repository	Description
x402-backend	API server, 74 native endpoints, payment middleware, MCP server
x402-frontend	React + TypeScript UI, wallet connect
x402-bazaar-cli	`npx x402-bazaar` -- CLI with 7 commands
x402-sdk	TypeScript SDK for AI agents
x402-langchain	Python LangChain tools (this repo)
x402-fast-monetization-template	FastAPI template to monetize any Python function

Live: x402bazaar.org | API: x402-api.onrender.com