UnderIndex

Fiches vérifiées sur 60 sous-cultures de la mode de niche (années, marques clés, pièces iconiques, où acheter, fourchette de prix, et un AVERTISSEMENT sur ce avec quoi chacune ne doit pas être confondue), afin que Claude cesse de mélanger les esthétiques voisines. Le catalogue et une fiche d’exemple sont gratuits ; les fiches complètes coûtent 0,01 $ chacune via x402 (USDC sur Base).

GitHub

Documentation

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.