@fatstack/mcp-bridge

A stdio MCP server that relays to the hosted Fatstack catalogue, where agents discover tools and pay per call in USDC via x402 on Base.

The catalogue is served at https://www.fatstack.net/api/mcp over streamable HTTP. If your client speaks that, point it there directly — you do not need this package. This exists for clients that only speak stdio.

Use it

npx @fatstack/mcp-bridge

In a client config:

{
  "mcpServers": {
    "fatstack": {
      "command": "npx",
      "args": ["-y", "@fatstack/mcp-bridge"]
    }
  }
}

That gives you discovery: the catalogue, every tool, and what each one charges. Listing is free. Calling a paid tool returns that provider's own 402 quote, telling you the price, the asset and the payee.

Paying

To let the bridge complete paid calls, give it a wallet and a ceiling:

{
  "mcpServers": {
    "fatstack": {
      "command": "npx",
      "args": ["-y", "@fatstack/mcp-bridge"],
      "env": {
        "FATSTACK_AGENT_KEY": "0x...",
        "FATSTACK_MAX_PER_DAY": "0.50",
        "FATSTACK_MAX_PER_CALL": "0.01"
      }
    }
  }
}

FATSTACK_MAX_PER_DAY is required whenever a key is present. The process refuses to start without it, rather than defaulting to a number we chose for your money.

Payments are final. There are no refunds and no chargebacks. Fund a throwaway wallet with what you are willing to lose in a day, and no more.

| Variable | Required | Default | Meaning | | ----------------------- | ---------- | ---------------------------------- | --------------------------------------- | | FATSTACK_MCP_URL | no | https://www.fatstack.net/api/mcp | catalogue to relay to | | FATSTACK_AGENT_KEY | no | — | private key; omit for discovery only | | FATSTACK_MAX_PER_DAY | with a key | — | hard USD ceiling per UTC day | | FATSTACK_MAX_PER_CALL | no | — | refuse any single call dearer than this | | FATSTACK_NETWORK | no | base | base or base-sepolia |

What it does and does not do

It is a relay. It never mints a quote, never rewrites a price, and never becomes a payee — the same rule the hosted aggregator holds to. Payment goes wallet to wallet, from you to the provider.

Your key is read from the environment of the process you started, on your machine. It is never transmitted to Fatstack, and nothing here writes it anywhere.

An unreachable catalogue is reported as an error, never as an empty tool list. Those two look identical to a client that cannot tell them apart, and only one is worth retrying.

Licence

MIT.