mcp-wallet-signer

Your private keys never leave your browser. Every transaction requires explicit approval in your own wallet (MetaMask, Rabby, TronLink, …).

Most blockchain tooling wants a private key in a config file — full, unsupervised access to your funds. These packages route each request to the browser wallet you already use, so you review and approve it like any other dapp interaction.

Packages

All three spawn browser-web3-signer serve, which owns the localhost bridge, the approval page and the browser tab. The binary for your platform is installed as a dependency; nothing else to set up.

MCP server

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

Or, for Claude Desktop / Cursor / Windsurf and any other stdio MCP client:

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

EVM_MCP_DEFAULT_CHAIN sets the chain id used when a call omits one (default: 1).

Libraries

import { WalletSigner } from "browser-evm-signer";

const signer = new WalletSigner({ defaultChainId: 8453 });
const { address } = await signer.connectWallet();
const { txHash } = await signer.sendTransaction({ to: "0x…", value: "1000000000000000000" });

Related MCP server: agent-wallet

What changed in the shims

• Gone: PendingStore, pendingStore, createHttpServer, startTestServer, buildConnectUrl, buildSignUrl, openBrowser — the in-process HTTP bridge they drove no longer exists.

• approvalUrl is now the bridge's base URL. The bridge opens the approval page itself and does not hand the per-request URL back.

• port (the constructor option) is ignored: the bridge binds its own free port. getPort() / DEFAULT_PORT still resolve, for source compatibility.

• MCP: the balance tools (get_balance, get_token_balance) and the TRON tools are gone from the MCP server. Balances never needed a wallet — any RPC-reading MCP server or cast call does them without an approval prompt — and TRON signing is a CLI away. WalletSigner.getBalance and .getTokenBalance are untouched in both libraries.

• Deprecated on npm and JSR. browser-evm-signer@0.3.0 never worked at all: its exports pointed at ./esm/mod.js while the tarball shipped ./esm/browser-evm-signer/src/mod.js, which took mcp-wallet-signer@0.6.0 down with it (#2).

The pre-shim Deno implementation — the in-process bridge, the Svelte approval UI, the wallet-signer-core package — is in the history, up to commit 636fd3b.

Development

npm install
npm test     # builds, then runs each package's tests against a fake bridge

Releases are per package: tag <package>@<version> and publish a GitHub release.

License

MIT