What is A2A protocol and how is it used in advertising?

A2A (Agent-to-Agent) is a communication protocol published by Google in 2025 that defines how autonomous software agents discover, authenticate and exchange structured messages with each other. In advertising, A2A provides the communication layer that allows a buyer agent and a publisher agent to interact across different technology platforms without requiring custom integration between each pair. A2A handles the messaging; the deal governance layer above it handles what is agreed and how it is recorded.

A2A, or Agent-to-Agent protocol, is an open specification published by Google in April 2025 that defines how autonomous software agents communicate with each other across different systems and platforms. It covers agent discovery (how agents find each other), authentication (how agents establish trust), task delegation (how one agent assigns work to another), and message structure (how agents exchange information in a format each can parse).

In advertising, A2A provides the communication layer for buyer agents and publisher agents to interact without requiring custom integrations between each pair of platforms.

At a glance

A2A protocol: Google's 2025 specification defining how AI agents communicate with each other across different platforms and systems, using a common message format.

MCP: Model Context Protocol — Anthropic's 2024 specification for how AI models connect to tools and data sources; complementary to A2A, which governs agent-to-agent communication.

Agent task: A unit of work one agent assigns to another via A2A, with a defined scope, input, and expected output; the receiving agent reports status updates until the task is complete.

Interoperability: The ability of agents built by different vendors to communicate and transact with each other through a shared protocol, without proprietary integration work.

What problem does A2A solve?

Before A2A, every attempt at agent-to-agent interaction in advertising required bilateral technical agreements between platforms. A DSP wanting its agent to communicate with an SSP's agent would need to agree on message formats, authentication mechanisms and error handling protocols with that specific SSP. Scale that across the number of DSP and SSP combinations in the market, and the integration burden becomes the barrier to adoption.

A2A provides a common standard. A buyer agent built to the A2A specification can interact with any publisher agent also built to the specification, without additional integration work. The same pattern enabled the modern programmatic ecosystem: OpenRTB standardised auction communication, and the market scaled from there. A2A is an attempt to do the same for agent-to-agent negotiation.

How does A2A work in an advertising context?

A buyer agent using A2A first discovers available publisher agents through an agent registry or a known endpoint. It authenticates with the publisher agent using the credentials and trust mechanisms the specification defines. It then initiates a task: in an advertising context, this might be a deal enquiry, a negotiation exchange or a delivery confirmation request.

The publisher agent receives the task, processes it within its own system, and returns a response. That response might be an inventory availability confirmation, a counter-offer on deal terms, or a delivery report. The A2A specification defines the structure of these exchanges so both agents can parse them without custom logic.

What does A2A handle and what does it not handle?

A2A handles the communication layer: discovery, authentication, and structured message exchange. It does not define what constitutes a valid advertising deal, how deal terms should be structured, or how disputes between agents should be resolved. Those questions are addressed by specifications at a higher layer.

The AAMP (Agentic Advertising Management Protocols), advanced by the IAB Tech Lab in 2025, sits above A2A. AAMP defines what a machine-readable advertising deal must contain: pricing terms, inventory specifications, targeting parameters, approval rights and audit fields. A2A is the channel through which agents communicate. AAMP is the vocabulary they use to discuss deals. Both are necessary for agent-to-agent advertising transactions to work reliably.

Is A2A in use in advertising today?

A2A was published in April 2025 and adoption in advertising is in early stages as of October 2026. The major DSP and SSP platforms have announced compatibility with A2A as part of their agentic roadmaps, but live production deployments of agent-to-agent deal negotiation using A2A are limited to specialist platforms and pilot programmes at this stage.

The adoption curve follows the pattern of OpenRTB, which took several years to reach widespread implementation after publication. A2A's trajectory will likely be faster given the existing infrastructure of the programmatic ecosystem, but meaningful standardisation across the market is a 2027-2028 timeframe based on current deployment rates.

What should advertising technology teams know about A2A?

Teams evaluating agentic advertising infrastructure should treat A2A compatibility as a baseline capability, not a differentiator. It is the equivalent of OpenRTB support in 2015: necessary to participate in the emerging ecosystem, but not sufficient to determine quality or governance.

The questions that matter are above the protocol layer: what deal governance does the platform provide, what does the deal record look like, and how are disputes between agents resolved? A platform that speaks A2A but cannot produce a bilaterally verifiable deal record is not meaningfully more capable than one that does not.

Frequently asked questions

How do AI agents communicate with each other in advertising?

AI agents communicate via shared protocols — primarily Google's A2A specification and the IAB Tech Lab's AAMP — that define the message format for deal enquiries, counter-proposals, and acceptances in machine-readable form.

What is the difference between A2A and MCP?

A2A (Agent-to-Agent) governs how agents communicate with each other — peer-to-peer messaging between AI systems. MCP (Model Context Protocol) governs how an agent connects to tools and data sources. Both are needed in a complete agentic advertising stack.

What protocols let advertising agents transact directly?

The primary standards are A2A for agent communication and AAMP (Agentic Advertising Management Protocols) for deal term structure. A2A handles the messaging layer; AAMP defines what a machine-readable deal must contain. Most agentic marketplace platforms implement both.