UnderIndex

60のニッチなファッションサブカルチャーに関する検証済みレコード（年代、主要ブランド、代表的なアイテム、購入先、価格帯、そしてそれぞれが混同してはならないものに関する警告）により、Claudeが隣接する美学を混同するのを防ぎます。カタログとサンプルレコードは無料で、完全なレコードはx402上で1件あたり$0.01（Base上のUSDC）です。

GitHub

ドキュメント

UnderIndex MCP server

Gives Claude (or any MCP client) verified records on 60 niche fashion subcultures: years, key brands, iconic items, music, where to buy, a price range, and a WARNING note on what each one must not be confused with. It is the UnderIndex API as three tools.

Tool	Cost	What it does
`list_subcultures`	free	Every slug with its name and years
`get_sample_record`	free	One complete record (Goth Ninja), to see the shape
`get_subculture`	$0.01 USDC on Base	One record, paid automatically over x402

Without a wallet key the two free tools work and get_subculture explains how to enable payments.

Install

Requires Node.js 20 or later. Nothing to download: npx fetches the underindex-mcp package on first run.

Claude Desktop

Add this to claude_desktop_config.json (Settings → Developer → Edit Config):

{
  "mcpServers": {
    "underindex": {
      "command": "npx",
      "args": ["-y", "underindex-mcp"],
      "env": {
        "UNDERINDEX_PRIVATE_KEY": "0x..."
      }
    }
  }
}

Claude Code

claude mcp add underindex -e UNDERINDEX_PRIVATE_KEY=0x... -- npx -y underindex-mcp

Leave out UNDERINDEX_PRIVATE_KEY to use only the free tools.

Configuration

Variable	Default	Notes
`UNDERINDEX_PRIVATE_KEY`	none	Private key of an EVM wallet holding USDC on Base. Use a dedicated wallet with a few dollars in it, never your main one.
`UNDERINDEX_MAX_PER_CALL`	`$0.05`	Hard cap per lookup. The server refuses to pay more than this, whatever the API asks.
`UNDERINDEX_API_URL`	`https://underindex-api.onrender.com`	Point it at a self-hosted server, e.g. one running on Base Sepolia testnet.

An unknown slug returns 404 before any payment is requested, so typos cost nothing. Each paid answer ends with a link to the payment on BaseScan.

Try it for free

The API's own server starts on Base Sepolia testnet when self-hosted, where test USDC is free from a faucet. Run it as described in the main README, then set UNDERINDEX_API_URL=http://localhost:3000 and a testnet wallet key.