Facilitator (x402)

A facilitator is the component in the x402 payment flow that verifies a submitted payment is valid and settles it on the blockchain, returning a confirmation to the resource server. It sits between the server selling access and the chain where payment lands, handling everything crypto-specific so the server does not have to.

The design goal is separation of concerns: the resource server decides what costs what; the agent's wallet decides whether to pay; the facilitator answers exactly one question — "did this payment actually go through?" — and makes it go through.

When an agent calls a paid endpoint without payment, the server responds with HTTP 402 and a payment requirement: amount, currency, and address. The agent's wallet signs a payment authorization and retries the request with it attached.

The server forwards that payload to its facilitator. The facilitator checks the signature, amount, and recipient, submits the USDC transfer to Base, and waits for confirmation — roughly two seconds. It then tells the server the payment settled, the server runs the handler, and the response goes back with a signed receipt and the transaction hash.

Without a facilitator, a server selling per-call access would need to run or rent a Base node, parse and validate signed payment payloads, submit transactions, monitor confirmations, and handle chain-specific failure modes like gas estimation and reorgs. That is a payments engineering team's worth of work to sell ten-cent tool calls.

With one, the integration collapses to an API call: forward the payment payload, get back settled-or-not. The server's private keys stay out of the request path, since funds flow to the seller's receiving address on-chain rather than through the server process.

The facilitator is trusted to report settlement honestly, but its claims are independently checkable: every settled payment is a public transaction on the Base settlement layer, so a seller can audit that reported revenue matches on-chain transfers. In x402, signed Ed25519 receipts give the paying agent the same auditability from the buyer's side.

This is a meaningfully weaker trust requirement than card processing, where the processor controls funds, can reverse them for 120 days, and is the only record of what happened. A facilitator coordinates; the chain decides.

When a seller claims an MCP server or API listing on the Loomal Index and attaches a per-call price (minimum $0.01), Loomal's payment infrastructure plays the facilitator role: verifying agent payments, settling USDC on Base, and issuing signed receipts — with a 5% fee on settled transactions, currently waived.

The seller's only jobs are owning the listing and running the handler. Verification, settlement, and receipt generation happen in the payment path before the handler is ever invoked, so unpaid calls never consume the seller's compute.