Published: 17 September 2026

TL;DR: A tamper-proof deal record has three structural properties: it is written at the moment of agreement rather than reconstructed later; it is held by both parties independently rather than only by the marketplace; and it is held by a neutral marketplace that has no commercial interest in altering it. Marketplace neutrality is the key structural condition. Tamper-proof does not mean perfect delivery compliance: it means the agreed terms cannot be altered after the fact without detection.

The claim that a deal record is tamper-proof is only meaningful if you understand what structural properties make it so. The term is used loosely in discussions of agentic advertising. Some providers use it to mean technically difficult to alter. Others use it to mean auditable. Neither definition captures the full picture.

A genuinely tamper-proof deal record has three properties that together make alteration both detectable and commercially pointless. This piece explains each one.

Written at the Moment of Agreement

The first property is timing. A deal record that is written at the moment buy-side and sell-side agents reach agreement is structurally different from a record reconstructed after the campaign ran.

Post-campaign reconstruction relies on platform logs: delivery data, bid records, and impression timestamps generated by systems controlled by one party. The party controlling those systems could, in principle, alter, omit, or reframe entries in ways that reflect a more favourable interpretation of what happened. Even without deliberate manipulation, reconstruction from logs introduces ambiguity because the logs were not written with the specific purpose of capturing agreed terms.

A record written at negotiation time captures the agreed terms in the moment those terms were established. Neither party has yet delivered anything. Neither party has any information about how the campaign will perform. The record reflects agreement, not outcome. This makes it much harder to argue that the record was shaped by knowledge of what happened later.

The Alkimi DealSheet is written by the marketplace at the moment the buy-side and sell-side agents reach agreement. The timestamp is applied at that moment. This is the foundational property from which the others follow.

Held by Both Parties Independently

The second property is custody. A deal record held only by the marketplace is better than no record, but it is not fully tamper-proof. The marketplace controls access to it. If the marketplace were to alter the record, the party relying on marketplace retrieval would have no way to detect the alteration.

A record held by both parties independently changes this. The buy-side agent receives a copy at the time of agreement. The sell-side agent receives a copy at the same time. These copies are independent: each party stores their copy in their own systems, outside marketplace control.

If the marketplace subsequently altered its own copy of the record, the change would be detectable by comparing the marketplace's version against the copy held by either party. The alteration would create a discrepancy. That discrepancy is evidence of tampering.

This bilateral custody model is what Alkimi provides. Both agents receive a DealSheet at the moment of agreement. Neither party's copy is held only by the marketplace.

Held by a Neutral Marketplace

The third property is neutrality. The first two properties describe how a record can be made resistant to alteration. The third property addresses why a marketplace might want to alter a record in the first place.

A marketplace that earns revenue based on deal values has a financial interest in deal outcomes. In a dispute, the marketplace might prefer a particular resolution that protects its revenue. A marketplace with that conflict is not a neutral custodian of the deal record.

A neutral marketplace earns its position by providing infrastructure: identity verification, proposal routing, deal record storage, and retrieval access. Its revenue is not tied to deal terms. It has no financial preference for one outcome over another in a dispute. This structural neutrality removes the commercial motive to alter records.

Alkimi is built as a neutral marketplace. Its revenue model is independent of the deal terms negotiated through it. This is not a policy commitment: it is a structural property of the business model.

What Tamper-Proof Does Not Mean

Tamper-proof refers specifically to the agreed terms. A tamper-proof deal record guarantees that the terms both parties agreed cannot be altered after the fact without creating a detectable discrepancy.

It does not guarantee that delivery matched the agreed terms. An advertiser's campaign can still underdeliver. A publisher can still serve inventory that falls outside the agreed scope. These are delivery failures, not deal record failures. The DealSheet is the reference point for identifying and quantifying delivery failures; it does not prevent them from occurring.

The value of the tamper-proof deal record is that it converts delivery disputes from arguments about what was agreed into arguments about measurement. That is a much more tractable dispute. Both parties have the agreed terms in front of them. The question is whether the delivery data matches.

The combination of timely writing, bilateral custody, and marketplace neutrality is what makes a deal record genuinely tamper-proof. Any one of the three properties on its own is insufficient. Together, they create a record that both parties can rely on as evidence of what was agreed, regardless of what happens during or after campaign delivery.