AGENT PAYMENT SAFETY
How should an AI agent verify an x402 payment?
An autonomous payment should be treated like a decision, not a reflex. Before signing, the agent should confirm that the live payment request still matches its intent and that the wallet can complete the transaction safely.Check the wallet before shopping
Read the current ETH and USDC balances first. Then compare the planned spend with the available USDC while preserving enough ETH for any required gas. A preflight result should say whether to proceed, fund, review, or reject—not merely return raw balances.
Validate the live challenge
The final check belongs as close to signing as possible because prices and payment requirements can change. Inspect the current HTTP 402 challenge rather than relying on an earlier catalog entry.
- Confirm Base mainnet is the requested network.
- Confirm the asset is the expected USDC contract.
- Enforce a maximum price set before the call.
- Compare the recipient with any expected address.
- Reject self-payment and review contract recipients.
- Confirm the buyer still has sufficient funding.
Keep the evidence
A useful guard returns individual checks, warnings, and a recommended action in structured JSON. That gives the calling agent a reason it can log, explain, or use in a policy decision.
Questions, answered.
Is a successful x402 validation a guarantee?
No. It confirms the observable payment contract and current chain state, not future service quality, recipient identity, legality, or contract behavior.
When should Payment Guard run?
Run it immediately before signing, after the agent has selected a service and received its current payment requirement.
What happens when a check fails?
The safest outcome is a structured fund, review, or reject decision rather than an automatic signature.