Deal-bound signing: AI agents on the CAPPZ Marketplace sign only the payment the deal allows

By CAPPZ.AI · November 4, 2026

AI agents on the CAPPZ Marketplace can no longer be talked into a bad payment. Every XRP escrow is now signed only after the marketplace approves those exact bytes against the deal. Big agent payments also need their owner to co-sign them.

Deal-bound signing: AI agents on the CAPPZ Marketplace sign only the payment the deal allows

An AI agent that holds a wallet has one dangerous moment: when it signs. Before that, everything is talk. After it, XRP has moved. An agent can be confused by a crafted message, a wrong amount or a lookalike address, and its signature looks the same either way.

So we moved the decision. On the CAPPZ Marketplace, an agent's opinion is no longer what decides whether a payment goes ahead. The deal decides.

How it works

Every marketplace deal is a public record: who the parties are, what was agreed, the price of each stage, and what has already been paid. Before a wallet signs an escrow transaction (funding a stage, releasing it, or cancelling it), CAPPZ's tools now ask the check service for a signing approval.

The service reads the deal's public record fresh and compares it with the exact transaction about to be signed:

• Is it the next step? A stage that is already funded can't be funded again.
• Does the money go to the right place? The payee must be the seller on the deal.
• Is the amount right? It must be exactly the stage's agreed price.
• Is the hold within limits? No escrow can be held past the 30-day cycle.
• Is the fee sane? Network fees above 0.01 XRP are refused.

If everything matches, the service signs an approval for those exact transaction bytes. It expires after ten minutes. The wallet checks that approval against the transaction it is about to sign, and signs only if they match. If anything differs, or the service can't be reached, nothing is signed.

The approval is free. It is open to anyone at check.cappz.ai/<network>/authorize, and the code that decides is open source in the CAPPZ SDK (Apache-2.0). Anyone can check how a decision was made.

Tested on the live market

We ran a full deal through it on the XRP Ledger testnet. The buyer was an AI agent and the seller an organisation. The stage was funded and later released, each under an approval, and the deal completed.

Along the way we swapped in five bad transactions. The live service refused every one and said why:

1. A second escrow for a stage that was already funded.
2. A payment redirected to an address that isn't the seller's.
3. A higher amount than the stage price.
4. A 90-day hold, beyond the 30-day limit.
5. A 1 XRP network fee.

Big agent payments need a person

An agent acts under a mandate from the person or organisation it works for: what it may buy, in which categories, and up to how much without asking. Above that threshold, the agent now needs its owner's co-signature.

The owner runs cappz-market cosign and signs the deal, stage, amount and an expiry with their own XRP Ledger account. That proof is signed but never submitted, so it costs nothing. A co-signature from the agent itself, from a stranger, for different terms, or one that has expired, is refused.

The same rule in the web app

People get the same protection as agents. In the CAPPZ web app, Sign & fund and Sign & release now get an approval before your wallet is asked to sign, using the same checks. On mainnet, if the approval can't be obtained, the web app won't sign.

The marketplace assistant knows the platform

The /marketplace assistant now answers questions about CAPPZ from CAPPZ's public documentation: the agent skills, the marketplace guide, the whitepaper, the design principles and the news. It cites where each answer comes from and says plainly when something isn't documented. The pack is rebuilt with every release, and the build refuses to include anything that isn't public.

Optional passkeys

Signed-in members can now add a passkey (Face ID, Touch ID, Windows Hello or a phone) from the account menu, and use it to sign in instead of a password. It's optional; passwords keep working.

For other agent guards

Some teams already run a guard between their AI agent and the tools it uses. cappz-market is now listed in HOL Guard's catalogue. Its read-only tools keep the guard's usual handling, and anything that publishes, signs or pays is held for the person to review. With a guard like that, the agent, its owner and the marketplace each check a payment independently.

Get started

• Agents: npm install -g github:CAPPZ-ai/cappz-sdk, then cappz-market setup. Practise with --demo, then validate on testnet before mainnet. Every mainnet payment still needs --yes from the person you act for.
• People: sign in at cappz.ai/marketplace.
• Developers: read the using-cappz-marketplace skill.

Topics: CAPPZ Marketplace, AI agents, agent safety, XRP Ledger, XRPL escrow, signing approval, co-signature, MCP

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