How MCP payments work
The Model Context Protocol gives AI agents a standardized way to call external tools — including financial tools. Here is the complete technical flow from the moment an agent decides to make a payment to on-chain settlement on Hedera.
What MCP is and why it matters for payments
The Model Context Protocol (MCP) is an open standard introduced by Anthropic in November 2024 that enables AI agents to securely connect to external systems through a standardized interface. Think of it as HTTP for AI agents — a universal protocol that defines how an agent discovers what tools are available, how to call them, and how to interpret the results.
Before MCP, every AI agent needed custom integration code for every tool it used. MCP eliminates this by providing a single interface both sides implement: the agent implements the MCP client, the tool provider (like BananaCrystal) implements the MCP server.
The MCP payment architecture
| Layer | Component | What it does |
|---|---|---|
| 1. Agent | Any MCP client (LangChain, Claude, GPT, custom) | Decides it needs to make a payment. Calls the MCP tool. |
| 2. MCP Transport | JSON-RPC 2.0 over persistent connection | Formats the tool call as a structured JSON-RPC request. |
| 3. MCP Server | agentic.bananacrystal.com/mcp | Receives the request, validates the API key and scope, routes to the handler. |
| 4. Guardrails | BananaCrystal policy engine | Checks spending limits, allowlists, idempotency keys before any funds move. |
| 5. Settlement | Hedera blockchain | Executes the on-chain transaction. Returns hash and confirmation in <5 seconds. |
The complete payment flow, step by step
transfer_tokens MCP tool
and constructs the arguments: recipient, amount, token
symbol, and memo.
transfer scope?), and
routes to the transfer handler.
How guardrails work inside MCP
Every BananaCrystal MCP tool call passes through a policy engine before any funds move. The guardrails are:
- Scope check — does the API key have permission for this operation?
- Spending limit check — would this transaction exceed the per-tx or daily cap?
- Allowlist check — is the recipient on the permitted list?
- Idempotency check — has this exact request been processed before?
- OTP verification — for transfers above a threshold, an OTP is required
Settlement on Hedera
BananaCrystal settles all transactions on Hedera blockchain — chosen specifically for agent payment infrastructure because it provides absolute finality in 3–5 seconds at $0.001 average fee. Unlike Ethereum's probabilistic finality, Hedera transactions are either settled or rejected with certainty.
The 10 BananaCrystal MCP tools
| Tool | Scope | What it does |
|---|---|---|
| get_balances | read_only | Check wallet balance for any token |
| get_exchange_rate | read_only | Get live buy/sell rates for any currency |
| get_transaction_history | read_only | Categorized transaction history |
| get_my_limits | read_only | Current spending limits and usage |
| transfer_tokens | transfer | Send stablecoins to any recipient |
| swap_currency | swap | Swap between 150+ currency stablecoins |
| initiate_deposit | fiat | Deposit fiat via bank wire or ACH |
| request_withdrawal | fiat | Withdraw to bank account |
| get_kyc_status | read_only | Check KYC verification status |
| initiate_kyc | fiat | Start KYC verification flow |