Wallet Signer

npm version License: MIT MCP Badge

Your private keys never leave your browser. Every transaction requires explicit user approval in your wallet.

Most blockchain MCPs require you to paste a private key into a config file — giving the AI agent full, unsupervised access to your funds. MCP Wallet Signer takes a different approach: it routes every transaction to your actual browser wallet (MetaMask, Rabby, etc.) via EIP-6963, so you review and approve each action just like any other dapp interaction. No keys in config files, no risk of silent transactions.

Compatible With

Works with any MCP-compatible client via stdio transport.

Installation

Claude Code CLI

claude mcp add evm-wallet -- npx -y mcp-wallet-signer

Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "evm-wallet": {
      "command": "npx",
      "args": ["-y", "mcp-wallet-signer"]
    }
  }
}

Run directly

npx -y mcp-wallet-signer
pnpx mcp-wallet-signer
bunx mcp-wallet-signer

MCP Tools

Tool	Description	Browser Required
connect_wallet	Connect wallet, return address	Yes
send_transaction	Send ETH/tokens, call contracts	Yes
sign_message	Sign arbitrary message (personal_sign)	Yes
sign_typed_data	Sign EIP-712 typed data	Yes
get_balance	Read ETH balance (via RPC)	No

How It Works

1. Agent calls an MCP tool (e.g., send_transaction)
2. Server opens browser to a local signing page
3. User connects wallet and approves the action
4. Result (address, tx hash, signature) returned to agent

Connect Wallet	Send Transaction	Sign Message

Supported Chains

Built-in RPC URLs for:

• Ethereum (1)
• Sepolia (11155111)
• Polygon (137)
• Arbitrum One (42161)
• Optimism (10)
• Base (8453)
• Avalanche (43114)
• BNB Smart Chain (56)

Configuration

Environment variables (optional):

Variable	Description	Default
EVM_MCP_PORT	HTTP server port	3847
EVM_MCP_DEFAULT_CHAIN	Default chain ID	1

Packages

This is a monorepo with two packages:

Package	Description
browser-evm-signer	Standalone library — sign EVM transactions via browser wallet, no MCP dependency
mcp-wallet-signer	MCP server — exposes browser-evm-signer as MCP tools for AI agents

Use browser-evm-signer directly if you want browser-based signing in your own Node.js/Deno app without MCP.

Development

Requires Deno v2.0+.

# Install all dependencies
deno task install:all

# Type check + lint + format check (both packages)
deno task check:all

# Run tests
deno task test:all

# Build both npm packages
deno task build:all

# Format code
deno task fmt

Project Structure

packages/
├── browser-evm-signer/     # Standalone signing library (npm: browser-evm-signer)
│   ├── src/                 # Library source
│   ├── web/                 # Svelte approval UI
│   ├── tests/               # Unit, e2e, and browser tests
│   └── scripts/build-npm.ts
│
└── mcp-wallet-signer/       # MCP server layer (npm: mcp-wallet-signer)
    ├── src/                  # MCP tool definitions + CLI entry
    └── scripts/build-npm.ts

Both packages are built with dnt and use node: builtins (no Deno-specific APIs) so the npm bundles run under Node.js.

License

MIT