A2A (Agent-to-Agent Protocol)

If MCP is a protocol that "connects agents and tools," then A2A is a protocol that "connects agents with each other."

A practical scenario makes this easier to understand. A sales support agent analyzes prospective customers, passes the results to a marketing agent to design an optimal campaign, and then a CRM agent updates the customer database — the A2A specification is what enables this kind of multi-agent coordination.

A2A defines four main functional areas:

Capability Discovery: A mechanism by which each agent publishes metadata about "what it can do," allowing other agents to search and reference that information.

Task Delegation: The request/response format used when one agent assigns a task to another agent.

State Synchronization: A streaming mechanism for sharing the progress and intermediate results of long-running tasks in real time.

Authentication and Authorization: A security layer that establishes trust relationships between agents and prevents unauthorized access.

In February 2026, NIST announced the AI Agent Standards Initiative, marking the beginning of full-scale standardization efforts based on A2A and MCP. As multi-agent systems move into practical use, the importance of A2A will only continue to grow.