TL;DR: AdCP, the Agent Communication Protocol published by IAB Tech Lab, is the technical standard that defines how advertising agents communicate for bilateral deal negotiation. It specifies the format for agent identity credentials, the schema for deal proposals and counter-proposals, the message types for each stage of a negotiation, and the structure of the bilateral deal record. It is the foundation for interoperable agent-to-agent advertising across different platforms and systems.

AdCP stands for Agent Communication Protocol. It was developed and published by IAB Tech Lab, the technical standards body for the digital advertising industry. AdCP is to agent-to-agent deal negotiation what OpenRTB is to auction-based programmatic: the common language that allows systems built by different vendors to communicate without bespoke integration work for every pair of platforms.

Understanding AdCP matters because it is the technical layer that makes cross-platform agent-to-agent advertising possible. Without a shared protocol, a buy-side agent built by one vendor cannot negotiate with a sell-side agent built by another, even if both agents are described as "agentic" or "A2A-capable." The protocol is what makes the capability interoperable.

What AdCP specifies

AdCP is a multi-layer specification. It covers four functional areas.

Agent identity and credentials. Before any deal negotiation begins, both agents must identify themselves in a verifiable way. AdCP specifies the credential format: what claims an agent must make about its principal (the buyer or publisher it represents), the mandate scope under which it operates, and the marketplace or infrastructure through which it is connecting. These credentials are structured so that the receiving agent can verify them against a registry, rather than accepting a free-text name or self-declaration.

The credential structure is important for supply chain verification. The industry has learned from the conventional programmatic experience that self-declared identity without verification creates fraud risk. AdCP builds verification into the protocol layer, so identity checks happen automatically at the start of every negotiation rather than requiring a separate manual verification step.

Deal proposal schema. A deal proposal in the AdCP framework is a structured document with defined fields: inventory parameters (domain list, placement type, ad format), CPM terms (proposed price, currency, billing unit), audience data conditions, campaign period, delivery commitment, and approval scope. Each field has a specified data type and, where relevant, a defined set of valid values.

The schema is what allows agents to evaluate proposals autonomously. A buy-side mandate can define acceptable values for each field; the buy-side agent compares the sell-side agent's counter-proposal against those acceptable values and determines whether agreement is achievable without requiring a human to read and interpret the proposal text.

Negotiation message types. AdCP defines a set of message types: proposal, counter-proposal, acceptance, rejection, expiry, and escalation request. Each message type has a defined format and a defined set of required and optional fields. The protocol specifies the valid sequences of message types: a counter-proposal must follow a proposal or a prior counter-proposal; an acceptance must follow a proposal or counter-proposal; and so on.

This sequencing is what makes autonomous negotiation possible. The agents know what message types are valid at each point in the negotiation, and they know what each message type means. There is no ambiguity that requires a human to interpret.

Deal record format. When both agents reach agreement, AdCP specifies how the agreed terms are recorded in the DealSheet. The DealSheet is a structured document that contains the agreed values for every field in the final accepted proposal, plus the identity credentials of both parties and the timestamp of agreement. The deal record format is designed to be retrievable and parseable by either party independently, for post-campaign audit.

How AdCP relates to existing IAB Tech Lab standards

AdCP is designed to work alongside, not replace, existing programmatic standards. OpenRTB, Sellers.json, Buyers.json, and ads.txt remain the foundation for auction-based programmatic. AdCP adds the bilateral negotiation and deal record layer on top of this foundation.

Publishers that have implemented AdCP can accept agent-negotiated bilateral deals through the same infrastructure that handles their auction traffic. The deal record created by AdCP negotiation is separate from the auction record; it provides an additional channel for direct bilateral deals without requiring a separate technical infrastructure.

What AdCP means for buyers and publishers

For buyers, AdCP compliance in a buy-side agent means the agent can negotiate with any AdCP-compliant sell-side agent, across any marketplace that implements the standard. This is the same portability benefit that OpenRTB created for auction-based buying.

For publishers, AdCP compliance in their sell-side infrastructure means they can accept deal proposals from any AdCP-compliant buy-side agent, regardless of which platform that agent runs on. A publisher does not need a direct technical integration with every buyer's system; they need one AdCP integration with the marketplace.

For the industry as a whole, AdCP is the technical prerequisite for a functioning agent-to-agent media buying market. Without a shared standard, the market fragments into proprietary integrations that limit buyers and publishers to working within closed ecosystems. With AdCP, the market can work the way the internet was designed to work: any compliant participant can transact with any other compliant participant.