Discover & pay over MCP

Discover services and the buyer quickstart cover finding and paying for services over HTTP. If your agent speaks Model Context Protocol instead, it can do both jobs as tool calls: search CDP’s hosted Bazaar MCP server for a service, then pay for it through the same x402 loop, carried in MCP’s wire format rather than HTTP headers.

Discover with the Bazaar MCP server

The Bazaar exposes an MCP server so any MCP-compatible agent can search and call paid x402 endpoints:

https://api.cdp.coinbase.com/platform/v2/x402/discovery/mcp

Discovery is public. The endpoint is unauthenticated, so no CDP API key is required to connect or search. It exposes three tools:

Tool	Does
`search_resources`	Semantic search over the Bazaar catalog — same index and filters as the HTTP search endpoint, returned as MCP tool results instead of JSON over REST.
`proxy_tool_call`	Calls a discovered resource by `toolName` and arguments. If the resource requires payment, it returns a payment-required tool result instead of the resource, which your client resolves using the loop below.
`validate_endpoint`	Read-only diagnostics for an x402 URL: whether it’s reachable, returns `402`, and advertises a valid discovery block. Makes no payment.

Searching is free. Only proxy_tool_call against a paid resource triggers a payment, and it does so with the standard x402 MCP transport rather than a Bazaar-specific mechanism, so the client setup below covers it.

The payment loop over MCP

The full wire-level detail lives in the x402 Foundation’s MCP transport spec; this is the short version:

The client calls a paid tool with no payment attached.
The server returns a tool result with isError: true and a PaymentRequired payload — MCP’s equivalent of an HTTP 402 status and PAYMENT-REQUIRED header.
The client builds a payment payload and retries the same tool call, this time with it attached at _meta["x402/payment"] — MCP’s equivalent of PAYMENT-SIGNATURE.
The server verifies and settles the payment, then returns the tool’s real result with settlement info attached at _meta["x402/payment-response"] — MCP’s equivalent of PAYMENT-RESPONSE.

Pay for tool calls

Wrap your MCP client so this loop runs transparently around tool calls, paired with a CDP-managed wallet — no private keys or manual scheme registration. The same wrapped client works against any x402 MCP server, including the Bazaar’s proxy_tool_call.

TypeScript
Python

npm install @coinbase/cdp-sdk @modelcontextprotocol/sdk @x402/core @x402/evm @x402/mcp

@x402/mcp’s wrapMCPClientWithPayment wraps any MCP SDK Client; every other method stays a direct passthrough. CdpX402Client from the CDP SDK provisions its wallet lazily and signs payments automatically.

import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { SSEClientTransport } from "@modelcontextprotocol/sdk/client/sse.js";
import { CdpX402Client } from "@coinbase/cdp-sdk/x402";
import { wrapMCPClientWithPayment } from "@x402/mcp";

const payment = new CdpX402Client({
  environment: "development",
  // Bound what this agent can spend — see [Set spend limits](/x402/buyer/client-configuration#set-spend-limits).
  spendControls: {},
});

const mcp = wrapMCPClientWithPayment(
  new Client({ name: "my-agent", version: "1.0.0" }, { capabilities: {} }),
  payment,
  // autoPayment: true pays and retries automatically on a 402; false throws
  // instead, so you can inspect the price and pay manually.
  { autoPayment: true },
);

await mcp.connect(new SSEClientTransport(new URL("http://localhost:4022/sse")));
const report = await mcp.callTool("generate_report", { topic: "USDC on Base" });

Full runnable version, including wallet funding and a payment-approval hook: clients/mcp/simple.ts.

pip install "cdp-sdk" "x402[evm,mcp]"

The standard x402Client runs the same loop via create_x402_mcp_client. Give it a CDP-managed wallet by wrapping a CDP Server Wallet with EvmLocalAccount, then adapting it to the x402 signer protocol with EthAccountSigner — it registers just like a local key.

from cdp import CdpClient
from cdp.evm_local_account import EvmLocalAccount
from x402 import x402Client
from x402.mcp import create_x402_mcp_client
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact import ExactEvmScheme

account = await CdpClient().evm.get_or_create_account(name="my-agent")
signer = EthAccountSigner(EvmLocalAccount(account))

payment = x402Client()
payment.register("eip155:84532", ExactEvmScheme(signer))

async with create_x402_mcp_client(payment, "http://localhost:4022") as mcp:
    report = await mcp.call_tool("generate_report", {"topic": "USDC on Base"})

Full runnable version, including faucet funding: clients/mcp/simple.py.

Reference

For exact signatures and every configuration option, see the generated SDK reference.

What to read next

Want a wallet bundled in rather than bringing your own? See Agentic Wallet. Building on AWS Bedrock AgentCore? Its “Coinbase x402 Bazaar” Gateway target wires up this same endpoint — see AgentCore (AWS). Building the other side of this exchange, a paid MCP tool? See Charge over MCP.

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Discover with the Bazaar MCP server

The payment loop over MCP

Pay for tool calls

Reference

What to read next

​Discover with the Bazaar MCP server

​The payment loop over MCP

​Pay for tool calls

​Reference

​What to read next

Discover with the Bazaar MCP server

The payment loop over MCP

Pay for tool calls

Reference

What to read next