Agent2Agent, or A2A, is a communication pattern or protocol for one AI agent to interact with another agent. It typically defines how agents exchange messages, delegate tasks and coordinate actions while preserving each agent’s own context, permissions and runtime boundaries.
A2A as an agent-to-agent communication pattern
Agent2Agent, or a2a, is best understood as the interaction layer between autonomous agents, not as a single product feature. It defines how one agent can send messages, request work, and coordinate with another while each side still preserves its own runtime boundaries and decision context.
That separation matters because A2A is about inter-agent cooperation under constrained trust, where one agent may be able to ask for help but not inherit unrestricted authority. The protocol shape therefore influences how intent, context, and permissions move between systems, and how much a recipient can safely rely on a sender’s claims.
What A2A changes in multi-agent systems
In a multi-agent system, A2A is the connective tissue that lets specialised agents collaborate without collapsing them into one monolithic process. One agent may gather data, another may reason over it, and a third may execute a task, but the communication pattern determines whether those steps remain cleanly separated or blur into unsafe delegation.
That distinction is important for architecture. A2A can support modularity, scaling, and clearer ownership of each agent’s role, but it also creates an explicit trust boundary between peers. If that boundary is weak, a compromised or overreaching agent can influence other agents, amplify mistakes, or pass along malformed instructions.
Security properties of A2A messages and delegation
For A2A to be safe, the messages themselves need more than transport. Agents typically need to know who is speaking, what task is being requested, what context is being shared, and whether the request is within the sender’s legitimate scope. Those properties are what keep a coordination protocol from becoming an open-ended privilege conduit.
In practice, secure A2A design often revolves around signed agent descriptors, task-scoped authorisation, explicit delegation rules, and controls that limit what can be requested mid-task. When the protocol includes webhooks or callbacks, the same design has to resist server-side request forgery and other abuse of outbound communication paths. The A2A Protocol Security Guide is the most direct reference for those controls, while Multi-Agent and A2A Security Guide covers the broader containment and delegation model around them.
Why A2A needs governance, observability, and trust boundaries
A2A is not just a messaging pattern, it is a governance problem when agents can act on behalf of users, other agents, or services. Once delegation is possible, teams need to know which agent owns which authority, how far that authority can travel, and how actions will be attributed after the fact.
That is why identity, authorisation, and runtime monitoring are so closely tied to A2A deployments. If an agent can relay work to another agent without clear policy limits, the system can drift into excessive delegation, opaque action chains, or hard-to-audit behaviour. The AI Agent Authorisation Guide helps frame the least-privilege side of that problem, and AI Agent Observability, Audit and Incident Response Guide shows how to trace agent actions when the chain spans multiple participants.
Risk and Threat Considerations
A2A increases the attack surface of agentic systems because it creates a path for one agent to influence another. If message authenticity, delegation scope, or callback handling is weak, attackers can abuse the protocol to escalate requests, redirect work, or trigger actions outside the intended trust boundary.
Failure mechanism: A malicious or compromised agent, or a forged peer interaction, can exploit weak identity binding, overbroad delegation, or unsafe webhook handling to move from coordination into unauthorised influence, persistence, or lateral control across agents.
Impact: The result can be delegated misuse, hidden task manipulation, data leakage through agent context, repeated unsafe actions across multiple agents, or a wider compromise that is harder to detect because it looks like normal inter-agent cooperation.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Agentic AI Top 10 and OWASP Non-Human Identity Top 10 address the attack and risk surface, while NIST SP 800-53 Rev 5 sets the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Agentic AI Top 10 | ASI03 — Identity & Privilege Abuse | A2A depends on delegated authority and cross-agent privilege boundaries. |
| Recommendation — Enforce per-task authority limits and verify each agent action against policy. | ||
| NIST SP 800-53 Rev 5 | IA-9 — Identification and Authentication (Non-Organizational Users) | A2A peers often authenticate as services or external agents across trust boundaries. |
| AC-6 — Least Privilege | A2A safety depends on limiting what one agent can ask another to do. | |
| Recommendation — Authenticate agent peers with strong service-to-service controls before permitting delegation. Constrain delegated agent permissions to the minimum required for each task. | ||
| OWASP Non-Human Identity Top 10 | NHI-04 — Insecure Authentication | A2A exchanges rely on authenticating agents and their signed requests correctly. |
| NHI-05 — Overprivileged NHI | A2A delegation becomes dangerous when an agent can pass excessive authority onward. | |
| Recommendation — Require robust agent authentication for every inter-agent exchange. Review agent scopes so delegated work cannot exceed the originating agent's authority. | ||
Practitioner Guidance
Why practitioners should care: A2A only works safely when each side can trust the other at the right level and for the right task. Treat the protocol as an authorisation boundary, not just a transport channel, because the main failure mode is not message delivery, it is delegated misuse.
What to watch for: Pay close attention to agent-to-agent requests that expand scope mid-task, callbacks that accept unauthenticated inputs, and coordination flows that cannot be cleanly attributed after execution. Those are the places where A2A systems most often lose containment.
Practitioner takeaway: A2A is strongest when it preserves modularity without letting trust become implicit, because every additional delegation hop should be more visible, not less.