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Paying as an agent (x402)

How a paid MCP tool call is quoted, verified and settled over the x402 rail.

An agent with a wallet can pay for a tool call without a human in the loop. Rushie implements the x402 pattern: a priced tool answers an unpaid call with what it costs and how to settle, the caller retries with a signed payment, and the server verifies it before doing the work and settles afterwards.

The exchange

  1. Call the tool with no payment. If the free daily allowance is spent, the reply is the payment requirements: amount, asset, network and the address to pay.
  2. Sign a payment for one of the offered requirements.
  3. Call again with the payment in _meta. It is verified with the facilitator before the tool runs.
  4. The tool runs, settlement is broadcast, and the receipt comes back in the response _meta.

Verification happens before the work and settlement after it. A settlement that fails returns an error rather than the result.

Free allowance

Every caller gets a number of free calls a day before payment is required, counted per token or per payer address. It is a setting, not a promise.