code-mode-alchemy-mcp

An MCP (Model Context Protocol) server that gives Claude access to Alchemy's blockchain APIs. Instead of defining 88+ individual tools, it loads all Alchemy API specs at startup and exposes just two tools — search and execute — keeping context usage minimal (~1,000 tokens vs. thousands).

Inspired by Cloudflare's Code Mode MCP pattern.

How It Works

At startup, the server fetches 10 Alchemy API specifications (6 REST OpenAPI + 4 JSON-RPC OpenRPC) and indexes all their endpoints. Claude can then:

Search — find relevant endpoints by keyword
Execute — run JavaScript code in a sandboxed environment against those endpoints

Claude → search("NFT owner") → finds getNFTsForOwner endpoint
Claude → execute(code)       → runs against Alchemy API, returns data

Loaded Specifications

REST (OpenAPI):

nft — NFT operations (mint, transfer, ownership queries)
portfolio — Wallet portfolio data
prices — Token pricing information
notify — Webhook notifications
transactions — Transaction history and details
accounts — Account management

JSON-RPC (OpenRPC):

transfers — Token transfer history (alchemy_getAssetTransfers)
token — Token metadata and balances (alchemy_getTokenBalances, etc.)
transaction-simulation — Simulate transactions before sending
bundler — ERC-4337 bundler operations

Prerequisites

Node.js 18+
An Alchemy API key

Installation

git clone https://github.com/your-username/code-mode-alchemy-mcp
cd code-mode-alchemy-mcp
npm install
npm run build

Configuration

Copy the example environment file:

cp .env.example .env

Set your values in .env:

ALCHEMY_API_KEY=your_key_here
ALCHEMY_NETWORK=eth-mainnet

Supported Networks

Any network string Alchemy supports in their URL format, e.g.:

eth-mainnet
eth-sepolia
polygon-mainnet
arb-mainnet
opt-mainnet
base-mainnet

Add to Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "alchemy": {
      "command": "node",
      "args": ["/absolute/path/to/code-mode-alchemy-mcp/dist/index.js"],
      "env": {
        "ALCHEMY_API_KEY": "your_key_here",
        "ALCHEMY_NETWORK": "eth-mainnet"
      }
    }
  }
}

Restart Claude Desktop. You should see the Alchemy MCP server connected.

Tools

`search(query, limit?)`

Searches across all loaded endpoint metadata (summaries, descriptions, paths, tags) and returns the most relevant endpoints.

| Parameter | Type | Default | Description | |-----------|------|---------|-------------| | query | string | required | Keywords to search for | | limit | number | 8 | Max results to return (max 20) |

Example queries:

"NFT owner" — find endpoints for fetching NFTs by owner
"token balance" — find token balance endpoints
"asset transfers" — find transfer history endpoints
"simulate transaction" — find simulation endpoints

`execute(code)`

Runs JavaScript code in a sandboxed Node.js VM with access to the Alchemy API. Execution is isolated with a 30-second timeout.

Available in the sandbox:

| Name | Type | Description | |------|------|-------------| | request(url, params?, options?) | function | Simplified API caller. Replaces {apiKey} and {network} in the URL automatically. | | fetch | function | Raw Fetch API for custom requests | | ALCHEMY_API_KEY | string | Your API key | | ALCHEMY_NETWORK | string | Your configured network | | console.log | function | Output captured and returned | | console.error | function | Errors captured and returned |

REST example:

const data = await request(
  "https://{network}.g.alchemy.com/nft/v3/{apiKey}/getNFTsForOwner",
  { owner: "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045", withMetadata: true }
);
return data;

JSON-RPC example:

const data = await request(
  "https://{network}.g.alchemy.com/v2/{apiKey}",
  {
    jsonrpc: "2.0",
    method: "alchemy_getTokenBalances",
    params: ["0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"],
    id: 1
  },
  { method: "POST" }
);
return data;

Usage Examples

NFTs for a wallet

"Show me all NFTs owned by 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"

Claude will:

Call search("NFT owner") → finds getNFTsForOwner
Call execute(...) → fetches and returns NFT data

Token balances

"What ERC-20 tokens does this address hold: 0x..."

Claude will:

Call search("token balances") → finds alchemy_getTokenBalances
Call execute(...) → returns token list with balances

Transaction history

"Show recent transactions for vitalik.eth"

Claude will:

Call search("asset transfers") → finds alchemy_getAssetTransfers
Call execute(...) → returns transfer history

Simulate a transaction

"What would happen if I sent 1 ETH from 0x... to 0x...?"

Claude will:

Call search("simulate transaction") → finds simulation endpoint
Call execute(...) → returns simulation result

Development

# Run in development mode (no build step needed)
npm run dev

# Build for production
npm run build

# Run the compiled server
npm start

Project Structure

code-mode-alchemy-mcp/
├── src/
│   └── index.ts        # Everything: spec loading, search, sandbox, MCP server
├── dist/
│   ├── index.js        # Compiled output (run this)
│   └── index.d.ts      # TypeScript declarations
├── .env.example        # Environment variable template
├── package.json
└── tsconfig.json

Architecture

Claude Desktop
     │
     │  MCP (stdio)
     ▼
MCP Server
     │
     ├── Startup: fetch 10 specs → index all endpoints
     │
     ├── search(query)
     │     └── score & rank endpoints by keyword match
     │
     └── execute(code)
           └── vm.runInNewContext() with 30s timeout
                 └── request() helper → Alchemy REST/RPC APIs

Why two tools instead of 88+?

Defining every Alchemy endpoint as a separate MCP tool would consume thousands of tokens just in tool definitions, before Claude even starts reasoning. This pattern loads specs once, searches them dynamically, and executes code — using ~1,000 tokens of tool definitions regardless of how many endpoints Alchemy adds.

Security Notes

Code in execute() runs in a Node.js vm sandbox with no access to the filesystem, environment, or require
The API key is injected by the sandbox via placeholder replacement — it is never returned in search results or exposed to user-visible output
Execution is limited to 30 seconds to prevent runaway code

References

Cloudflare Code Mode MCP — the pattern this is based on
Cloudflare Agents API Reference
Alchemy OpenAPI Specs
Model Context Protocol
Alchemy API Docs

License

MIT

code-mode-alchemy-mcp