x402 Seller

x402-seller-mcp

An MCP server that turns every paid endpoint of x402-seller — crypto prices, DeFi data, on-chain reads, web reading, Claude-powered text tasks — into a tool your agent (Claude Desktop, Cursor, or any MCP client) can call.

Tools are generated at startup from the server's own /.well-known/x402.json discovery document — not hand-listed — so the tool list always matches what's actually live on the origin.

Two modes

• No wallet configured (default) — calling a tool fetches the endpoint, gets back the real 402 Payment Required challenge, and returns a plain-language explanation (price, network, how to enable payment) instead of the actual data. Safe to try with zero setup.
• Wallet configured (BUYER_PRIVATE_KEY set) — calls are paid automatically over x402 (via @x402/fetch) and return the real result plus the settlement receipt (payer address, transaction hash).

Install

npx x402-seller-mcp

That's the whole install — nothing to clone, build, or configure to try it in explain-only mode.

Claude Desktop

Add this to your claude_desktop_config.json (Settings → Developer → Edit Config):

{  "mcpServers": {    "x402-seller": {      "command": "npx",      "args": ["-y", "x402-seller-mcp"]    }  }}

To enable automatic payments, add an env block (see Enabling payments below):

{  "mcpServers": {    "x402-seller": {      "command": "npx",      "args": ["-y", "x402-seller-mcp"],      "env": {        "BUYER_PRIVATE_KEY": "0x..."      }    }  }}

Restart Claude Desktop after editing the config.

Cursor

Cursor uses the same mcpServers shape — add the same block to ~/.cursor/mcp.json (or your project's .cursor/mcp.json), then reload the MCP servers from Settings → MCP.

Enabling payments

⚠️ Use a throwaway wallet, never a wallet holding significant funds. The private key you set here can sign USDC transfers on Base up to whatever price each tool call costs (all endpoints on this server are priced at $0.005–$0.02 per call) — but any process with the key in its environment can, in principle, use it. Generate a fresh wallet dedicated to this MCP server and fund it with a few dollars of USDC on Base, nothing more.

1. Generate a wallet (any EVM wallet works — e.g. with viem: node -e "const {generatePrivateKey,privateKeyToAccount}=require('viem/accounts');const k=generatePrivateKey();console.log(k, privateKeyToAccount(k).address)", or MetaMask/any wallet app export).
2. Send a small amount of USDC on Base (the network this server settles on) to that wallet's address — a few dollars covers hundreds of calls at these prices.
3. Set BUYER_PRIVATE_KEY to that wallet's private key (the 0x...-prefixed hex string) in your MCP client's config (see examples above) or in your shell environment if running the server directly.
4. Restart the MCP server (or your MCP client). Tool calls will now pay automatically and return real results.

Configuration

Tools

One tool per paid resource in the origin's discovery document, named <method>_<path> (e.g. get_api_gas_base, post_api_web_read). Run the server and call tools/list, or browse /.well-known/x402.json directly, for the current full list and per-tool input schemas — deliberately not duplicated here, since it would drift from the live origin.

Related

For a general-purpose agent that just wants a small set of everyday tools (fact verification, market data, gas price, quick AI tasks) instead of one tool per endpoint, see @dm2233/agent-data-mcp (npm) — it wraps this same 33-endpoint catalog as 5 grouped tools.

Development

git clone https://github.com/entreprisedaney33-rgb/x402-seller.gitcd x402-seller/mcpnpm installnode server.js          # runs on stdio, waits for a client

test/manual-test.mjs is a standalone harness that spawns the server exactly like an MCP client would (via StdioClientTransport) and drives it with the official Client class — listTools(), then callTool() in both modes. Run it directly with node test/manual-test.mjs after npm install (it reads BUYER_PRIVATE_KEY from the parent repo's .env if present, to exercise the paid path too).

License

MIT