MCP server (@flying-money/mcp)

Easiest: send your assistant the one message on Connect an assistant; it follows /agent.md and sets this up itself.

An MCP server that lets any MCP-capable agent (Claude Desktop or Claude Code, Hermes-based agents, and others) pay APIs from a budget its owner gives it, and ask its owner for one. The budget's limits are enforced on-chain, not by the prompt.

Start it with one setting

The only setting you need is your owner's wallet address:

claude mcp add flying-money -e FM_OWNER=0xYourWallet -- npx -y @flying-money/mcp

On first run the server makes its own spending key and keeps it in ~/.flying-money/agent-key (readable only by you). It never prints or returns the key. A spending key holds no money: it can only spend budgets its owner funds, and only at the seller each one names. Call fm_status to see your spending address.

Then, when a paid service needs a budget, fm_request_budget sends your owner a request (or gives you a link for them). The owner approves it in the app. Nobody copies keys or ids by hand.

Tools

Tool	Input	Output
fm_status	none	Your spending address and budgets: network, seller, amount, spent, remaining, end date (read-only)
fm_explain	none	Plain-language rules: who you can pay, how much, until when
fm_quote	url	The price and accepted networks, without paying
fm_paid_fetch	url, method?, body?, max_price?	The response and the payment. Refuses prices above max_price or the per-request cap
fm_request_budget	service, amount, days, reason	Asks your owner for a budget; moves no money
fm_request_status	requestId	Whether your owner approved it

There is no tool to give or top up a budget, and no tool returns the spending key. Only the owner can fund one, from their own wallet.

Settings (environment)

Variable
FM_OWNER	Your owner's wallet address, so you can ask them for budgets
FM_OWNER_GRANT	Optional: the owner's permission to send requests straight to their inbox (from People & agents in the app)
AGENT_KEY	Optional: bring your own spending key instead of the one the server makes
FM_KEY_FILE	Where the made key is kept (default agent-key next to FM_STORE)
AGENT_CERTIFICATES	Optional: budget ids already given to you, comma-separated
AGENT_CHAINS	Registry keys, comma-separated (default arbitrum-sepolia)
FM_MAX_PRICE	Per-request cap in USDC (default 0.05)
FM_STORE	Durable outbox file (default ~/.flying-money/outbox.json)

Until the package is published to npm, build it from the repository (pnpm install && pnpm build) and use node /path/to/flying-money/packages/mcp/dist/bin.js instead of npx -y @flying-money/mcp.

Claude Desktop

In claude_desktop_config.json:

{
  "mcpServers": {
    "flying-money": {
      "command": "npx",
      "args": ["-y", "@flying-money/mcp"],
      "env": { "FM_OWNER": "0xYourWallet" }
    }
  }
}

Any MCP client over HTTP

npx -y @flying-money/mcp --http 8788

This serves streamable HTTP at http://127.0.0.1:8788/mcp, for this machine only.

Notes

• max_price is checked against the seller's quoted price before paying. The per-request cap (FM_MAX_PRICE) and the budget's amount always apply.
• Failed requests are not charged: the seller turns the price into credit for your next request.