MCP Blockchain Server

An MCP server that lets AI assistants read blockchain data and prepare transactions — while the user keeps full custody of their keys and signs every transaction in their own wallet.

It runs as a single, self-contained process. No database, no Redis, no API keys, no separate frontend to build. Point your MCP client at it and go.

┌──────────────┐   MCP (stdio)   ┌─────────────────────┐   RPC    ┌────────────┐
│ AI assistant │ ──────────────► │  mcp-blockchain     │ ───────► │ Blockchain │
│ (Claude …)   │ ◄────────────── │  server             │ ◄─────── │  (EVM)     │
└──────────────┘                 │   + signing web page │          └────────────┘
                                 └─────────┬───────────┘
                                           │ opens link, signs in wallet
                                           ▼
                                     ┌───────────┐
                                     │   User    │  (MetaMask / Rabby / …)
                                     └───────────┘

Why this design

The hard problem in AI + blockchain is letting an assistant act without ever touching private keys. This server solves it by splitting the work:

• Reads (balances, contract state) happen server-side and return directly to the assistant.
• Writes are only ever prepared server-side. The server hands back a URL; the user opens it, reviews the details, and signs in their own wallet. The wallet broadcasts the transaction. The server only ever learns the resulting transaction hash. Private keys never reach the server.

Quick start

Requirements: Node.js 18+. No clone, no build, no API keys.

Add the server to any MCP client that launches stdio servers. For Claude Desktop, open Settings → Developer → Edit Config and add:

{
  "mcpServers": {
    "blockchain": {
      "command": "npx",
      "args": ["-y", "mcp-blockchain-server"]
    }
  }
}

Restart the client. You can now ask things like "What's the ETH balance of vitalik.eth?" or "Send 0.01 test ETH to 0x… on Sepolia." For a send, the assistant returns a link — open it, review, and sign in your wallet.

No configuration is required: the server ships with free public RPC endpoints and defaults to the Sepolia testnet.

Use it in other clients

The same npx command works anywhere that runs an MCP stdio server — the config shape is identical across clients:

{ "command": "npx", "args": ["-y", "mcp-blockchain-server"] }

This is the block to drop into Cursor (.cursor/mcp.json), Cline, Windsurf, VS Code (.vscode/mcp.json), and others. To pass options, add an "env" block (see Configuration).

Run from source (development)

git clone https://github.com/zhangzhongnan928/mcp-blockchain-server.git
cd mcp-blockchain-server
npm install      # installs and builds (via the prepare script)

Then point the client at the build instead of npx:

{ "command": "node", "args": ["/absolute/path/to/mcp-blockchain-server/build/index.js"] }

Remote / web clients (HTTP transport)

For MCP clients that connect over HTTP instead of spawning a local process, run the server in HTTP mode. It then serves the MCP endpoint and the signing page on one port:

MCP_TRANSPORT=http PUBLIC_BASE_URL=https://your-host npx -y mcp-blockchain-server

• MCP endpoint (Streamable HTTP): https://your-host/mcp
• Signing links: https://your-host/tx/<id>

Bind a public interface with HOST=0.0.0.0 (or keep the default 127.0.0.1 and put it behind a reverse proxy). When exposed publicly, set MCP_ALLOWED_HOSTS and/or MCP_ALLOWED_ORIGINS to enable DNS-rebinding protection, and front it with HTTPS and access control.

To host it as a custom connector (Docker, one-click Render, or a quick tunnel for testing) and wire it into Claude's Add custom connector dialog, see the deployment guide.

Tools

| Tool | Purpose | | --- | --- | | get-chains | List supported networks and their chain ids. | | get-balance | Native-token balance for an address on a chain. | | read-contract | Call a read-only contract method (pass an abi or set ETHERSCAN_API_KEY). | | prepare-transaction | Create an unsigned transaction and return a signing URL. | | get-transaction-status | Track a prepared transaction by id. |

read-contract is zero-config when you pass a human-readable ABI:

{
  "chainId": "1",
  "address": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
  "method": "balanceOf",
  "args": ["0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"],
  "abi": ["function balanceOf(address) view returns (uint256)"]
}

Signing flow

1. The assistant calls prepare-transaction. The server stores it and returns http://localhost:3000/tx/<id>.
2. The user opens the link. The page shows the network, recipient, amount, and calldata.
3. The user connects their wallet and clicks Approve & Sign. The wallet signs and broadcasts (eth_sendTransaction).
4. The page reports the transaction hash back to the server, which watches for on-chain confirmation.
5. The assistant polls get-transaction-status until it is CONFIRMED.

The signing page is plain HTML + vanilla JS served by the same process — there is nothing extra to build or deploy.

Configuration

Everything is optional. Copy .env.example to .env to override defaults.

| Variable | Default | Description | | --- | --- | --- | | MCP_TRANSPORT | stdio | stdio for local clients, or http to serve MCP over Streamable HTTP at /mcp. | | PORT | 3000 | Port for the signing web server (and the /mcp endpoint in http mode). | | HOST | 127.0.0.1 | Interface to bind (localhost only by default). Set 0.0.0.0 to expose remotely. | | PUBLIC_BASE_URL | http://localhost:<PORT> | Base URL used in signing links and the /mcp URL (set when hosting remotely). | | DEFAULT_CHAIN_ID | 11155111 | Default chain (Sepolia testnet). | | LOG_LEVEL | info | error | warn | info | debug (logs go to stderr). | | MCP_DATA_DIR | ~/.mcp-blockchain | Where pending transactions are stored. | | RPC_URL_<chainId> | built-in public RPC | Override the RPC for a chain, e.g. RPC_URL_1=https://…. | | INFURA_API_KEY | — | If set, upgrades default RPCs to Infura. | | ETHERSCAN_API_KEY | — | If set, read-contract can auto-fetch verified ABIs. | | MCP_ALLOWED_HOSTS | — | Comma-separated Host allowlist for http mode (enables DNS-rebind protection). | | MCP_ALLOWED_ORIGINS | — | Comma-separated Origin allowlist for http mode (enables DNS-rebind protection). |

Supported chains

Ethereum (1), Sepolia (11155111), Polygon (137), Polygon Amoy (80002), Base (8453), Base Sepolia (84532), Arbitrum One (42161), OP Mainnet (10). Each has a built-in public RPC; override any with RPC_URL_<chainId>.

Development

npm run dev        # run from source with auto-reload (tsx)
npm run build      # compile TypeScript to build/
npm start          # run the compiled server
npm test           # run the test suite (node:test)
npm run typecheck  # type-check without emitting

Releasing

CI (build + tests) runs on every push and PR. To publish a new version to npm:

1. Add an NPM_TOKEN repository secret (an npm automation token) — once.
2. Bump the version and tag: npm version patch (or minor / major), then git push --follow-tags.
3. Create a GitHub Release for that tag. The release workflow runs the tests and publishes to npm (with provenance).

You can also publish manually: npm publish.

Security

• Private keys never reach the server. It only prepares transactions; the user's wallet signs and broadcasts them.
• The signing server binds to localhost by default and sets a strict, nonce-based Content-Security-Policy on the signing page.
• All tool inputs (addresses, amounts, calldata) are validated before use.
• Logs are written to stderr so they never corrupt the MCP stdio stream.

See docs/security.md for details.

Documentation

• Getting Started
• Architecture
• Tools & HTTP API
• Security

License

MIT — see LICENSE.