anchor-x402-mcp

MCP server exposing 14 anchor-x402 services as tools any Claude Desktop / Cursor / Codex / Continue agent can call. Pay-per-use USDC via x402 on Base mainnet — no API keys, no subscriptions.

Two transports — pick by who holds the wallet key

This package (stdio) needs a funded EVM private key in the local process (ANCHOR_WALLET_PRIVATE_KEY) and pays for each call on your behalf. Convenient, but you are handing a hot key to a process.

Streamable HTTP — POST https://api.anchor-x402.com/mcp — needs no install and no key handover. It exposes all 18 services (four more than this package: roll_random, investigate_wallet, ledger_summary, ledger_report), and you pay per call with a PAYMENT-SIGNATURE header, so your key never leaves your side.

{
  "mcpServers": {
    "anchor-x402": { "url": "https://api.anchor-x402.com/mcp" }
  }
}

Clients that speak remote MCP natively take the url form above. For one that only launches stdio processes, bridge it:

{
  "mcpServers": {
    "anchor-x402": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://api.anchor-x402.com/mcp"]
    }
  }
}

Protocol revisions supported: 2026-07-28, 2025-11-25, 2025-06-18, 2025-03-26 — both the stateless era and the initialize handshake era, on one endpoint. server/discover and tools/list are free; tools/call is paid.

Payment is the ordinary x402 dance, surfaced inside MCP rather than around it: an unpaid tools/call returns a result (not a JSON-RPC error) with isError: true and the challenge in structuredContent.accepts, plus the canonical payment-required header. Sign one of the options and retry the identical call with PAYMENT-SIGNATURE. The challenge comes back as a result on purpose — an agent can read it and pay, whereas a JSON-RPC error would be swallowed by the client before the model ever saw it.

Server card: /.well-known/mcp/server-card.json. A worked client, including the adapter that bridges a stock x402 fetch wrapper to the MCP result shape, is in examples/agent/mcp-paid-call.mjs.

The rest of this README covers the stdio package.

What an agent gets

Fourteen tools, $0.001–$0.05 per call.

Commodity primitives (9, $0.001–$0.02):

Universal LLM endpoints (5, $0.01–$0.05) — added in v0.2:

The investigator (/v1/investigate, $1.77 async) and the hosted chatbot at chat.anchor-x402.com are not included in the MCP — they're accessed directly via the HTTP API and the browser respectively.

The MCP server pays for itself — your wallet gets debited automatically for each call. No prepay, no API key, no account.

Install

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "anchor-x402": {
      "command": "npx",
      "args": ["-y", "anchor-x402-mcp"],
      "env": {
        "ANCHOR_WALLET_PRIVATE_KEY": "0xYOUR_BASE_WALLET_PRIVATE_KEY"
      }
    }
  }
}

Restart Claude Desktop. Ask: "Anchor the hash 7646dda1564bde0ef3f3971f4c002962df64246da4aa1d8c47247e7632494710 on mainnet" — it'll call anchor_hash and pay $0.005 USDC from your wallet.

Claude Code

Add to your project's .mcp.json:

{
  "anchor-x402": {
    "command": "npx",
    "args": ["-y", "anchor-x402-mcp"],
    "env": {
      "ANCHOR_WALLET_PRIVATE_KEY": "0xYOUR_BASE_WALLET_PRIVATE_KEY"
    }
  }
}

Codex CLI (OpenAI)

Edit ~/.codex/config.toml:

[mcp_servers.anchor-x402]
command = "npx"
args = ["-y", "anchor-x402-mcp"]

[mcp_servers.anchor-x402.env]
ANCHOR_WALLET_PRIVATE_KEY = "0xYOUR_BASE_WALLET_PRIVATE_KEY"

Restart codex. Type /mcp to confirm anchor-x402 shows in the loaded servers list.

ChatGPT Desktop

Settings → Integrations → MCP servers → Add server. Paste:

{
  "command": "npx",
  "args": ["-y", "anchor-x402-mcp"],
  "env": {
    "ANCHOR_WALLET_PRIVATE_KEY": "0xYOUR_BASE_WALLET_PRIVATE_KEY"
  }
}

Save, restart, the 14 tools appear in any chat with tool-use enabled.

Cursor

Edit ~/.cursor/mcp.json (global) or <project>/.cursor/mcp.json (project-scoped):

{
  "mcpServers": {
    "anchor-x402": {
      "command": "npx",
      "args": ["-y", "anchor-x402-mcp"],
      "env": {
        "ANCHOR_WALLET_PRIVATE_KEY": "0xYOUR_BASE_WALLET_PRIVATE_KEY"
      }
    }
  }
}

OpenAI Agents SDK (programmatic)

from openai_agents import Agent, MCPServerStdio

mcp = MCPServerStdio(
    command="npx",
    args=["-y", "anchor-x402-mcp"],
    env={"ANCHOR_WALLET_PRIVATE_KEY": "0xYOUR_BASE_WALLET_PRIVATE_KEY"},
)
agent = Agent(name="researcher", model="gpt-4o", mcp_servers=[mcp])

Same package, same env, programmatic instead of config-driven.

Continue / Smithery / generic MCP client

Same shape — command: npx, args: [-y, anchor-x402-mcp], env carries your wallet key. The MCP SDK handles transport.

Or install via Smithery one-liner:

npx -y @smithery/cli install anchor-x402-mcp --client claude

(replace --client claude with cursor, codex, windsurf, etc.)

Run standalone

ANCHOR_WALLET_PRIVATE_KEY=0xYOUR_KEY npx anchor-x402-mcp

Speaks MCP over stdio. Pipe into any MCP-compatible client.

Funding your wallet

The wallet you set as ANCHOR_WALLET_PRIVATE_KEY needs USDC on Base mainnet. Any amount works — even $1 buys 100 anchor calls or 1000 commodity-tier calls. Send USDC to your wallet's Base address:

• USDC contract on Base: 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
• Bridge from Ethereum mainnet via bridge.base.org
• Buy directly on Coinbase and withdraw to Base

The MCP server signs payments via x402 — Coinbase's open HTTP-native micropayments protocol. Each request:

1. Hits an anchor-x402 endpoint
2. Gets a 402 with payment requirements
3. Server signs a USDC transfer authorization with your private key
4. Retries the request with the signed payment — the API settles via Coinbase's facilitator

You see the response, your wallet's USDC balance ticks down by the call price. Sub-second, no ledger, no account.

Environment variables

If ANCHOR_WALLET_PRIVATE_KEY is unset, paid tool calls return a friendly 402 message explaining how to set it. /health and /openapi.json (not exposed as tools, but reachable via direct curl) work without payment.

Security notes

• The private key lives in your MCP client's config file. Treat it like a hot wallet — only fund what you're willing to spend autonomously.
• Recommended: generate a fresh wallet specifically for agent use. Top up periodically; don't reuse a wallet that holds significant funds.
• The MCP server only signs USDC payment authorizations to anchor-x402's known treasury addresses (visible in the 402 response). It cannot drain your wallet to arbitrary addresses.
• Source code is fully open at github.com/hypeprinter007-stack/anchor-x402-mcp. Audit before installing.

Verifying anchor receipts

Every anchor_hash and attest_decision call returns Base + Solana tx URLs. These are independently verifiable on the public block explorers — agents can confirm an anchor exists without re-paying:

• Base: https://basescan.org/tx/<base.tx> — Input Data field contains the merkle root
• Solana: https://solscan.io/tx/<solana.tx> — Memo program data contains the same hex

The on-chain bytes are the receipt; the API response is just a convenience wrapper around them. See the on-chain verifiability primer for the full verification recipe.

Troubleshooting