Block Your AI Agent at the Network Level — It's Free

There's a 4-digit code on every card transaction that controls exactly what your AI agent can spend on. It's not the card number. It's not the CVV. It's the Merchant Category Code — and most fintech devs have never touched it. Every merchant has one. 5411 is grocery stores. 7372 is software. 4816 is computer network services. 7995 is gambling. Stripe Issuing exposes all of these in a single API field called allowed_categories. Here's what that unlocks for AI agents: you can issue a card that can only buy cloud infrastructure and dev tools — and physically cannot be used at a restaurant or casino. No app logic required. The card network enforces it at the transaction level. MCC 7372 and 4816 cover most of what a dev agent needs. Allow those two, block everything else, and your agent has a hardware-enforced budget that no prompt injection can override. Save this. Link in bio for the full MCC reference table.