The Agent2Agent (A2A) protocol, launched by Google Cloud on April 9, 2025, addresses the critical need for interoperability among AI agents, enabling them to collaborate autonomously across diverse enterprise data systems, applications, and frameworks. Developed with contributions from over 50 technology and service partners, A2A aims to facilitate secure communication, information exchange, and coordinated actions among AI agents, thereby enhancing productivity and automating complex workflows. The protocol complements Anthropic's Model Context Protocol (MCP) and draws on Google's expertise in scaling multi-agent systems.

The core methodology of A2A is guided by five key design principles:

1. Embrace Agentic Capabilities: A2A enables agents to collaborate in their natural, unstructured modalities, transcending limitations of shared memory, tools, or context, and supporting true multi-agent scenarios without constraining an agent to a "tool" role.
2. Build on Existing Standards: The protocol is engineered atop widely adopted web standards, specifically utilizing HTTP for foundational communication, SSE (Server-Sent Events) for real-time updates and long-running task feedback, and JSON-RPC for structured message exchange and remote procedure calls. This approach ensures easier integration with existing IT infrastructures.
3. Secure by Default: A2A incorporates enterprise-grade authentication and authorization mechanisms, providing parity with established OpenAPI authentication schemes, thereby ensuring secure agent interactions from its inception.
4. Support for Long-Running Tasks: The protocol is designed to manage tasks of varying durations, from immediate completions to those spanning hours or days (e.g., deep research with human-in-the-loop interventions). It provides continuous real-time feedback, notifications, and state updates throughout a task's lifecycle.
5. Modality Agnostic: Recognizing that agentic interactions extend beyond text, A2A supports various data modalities, including but not limited to audio and video streaming, allowing for richer and more versatile agent communications.

The operational flow of A2A involves a "client" agent formulating and communicating tasks to a "remote" agent, which is responsible for execution and response. This interaction is facilitated by several technical capabilities:

• Capability Discovery: Agents advertise their specific functionalities and services through an "Agent Card," a structured data object typically formatted in JSON. Client agents leverage these Agent Cards to programmatically identify and select the most suitable remote agent for a given task, forming a dynamic service discovery mechanism.
• Task Management: Communication is inherently task-oriented. A defined "task" object with a lifecycle governs the agent-to-agent interaction. For long-running operations, A2A enables robust state synchronization, allowing both client and remote agents to maintain awareness of the task's current status. The final output of a completed task is referred to as an "artifact."
• Collaboration: Agents exchange messages to convey contextual information, deliver replies, transmit artifacts, and relay user instructions. The protocol's messaging structure supports a rich dialogue between agents.
• User Experience Negotiation: Each message can include "parts," which are self-contained pieces of content (e.g., a generated image, a document, a video segment). Each "part" is explicitly typed with a content-type identifier. This allows client and remote agents to negotiate the optimal data format and facilitates explicit negotiation of user interface capabilities, such as the rendering of iframes, embedded video players, or interactive web forms within a unified user experience (e.g., an Agentspace environment).

The protocol is being released as open source, with a commitment to community contributions and a production-ready version planned for later in 2025. This open approach, combined with its adherence to existing web standards and comprehensive feature set, positions A2A as a foundational element for a new era of interoperable and collaborative AI agent systems.