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Discussion on: We checked 49 payment MCP servers. 37 can move money. Only 4 document a spending budget.

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whiteknightonhorse profile image
whiteknightonhorse •

A budget written in the docs or the prompt doesn't stop a tool call, so I'd check where the cap is enforced. In our setup it sits in the buyer's wallet client, and the server only accepts a payment that matches the quote it issued.

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azizanapp profile image
Azizan •

That is the right question to ask of any setup: where is the cap enforced? Putting it in the buyer's wallet client plus a server that only accepts a payment matching its own quote closes both ends, the agent cannot overspend and the merchant cannot overcharge. Out of interest, how do you handle a cap shared across several agents using different wallet clients?

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whiteknightonhorse profile image
whiteknightonhorse •

We don't solve that one yet. Each payment is checked against its own quote, so the server never sees what the other agents spent. A shared cap needs one place that sees every spend, and the simplest version I know is one funding wallet that hands each agent a capped allowance. Are you running into this with a real setup?