A2A Protocol

Python models for Google's Agent-to-Agent (A2A) Protocol specification. This package provides both Pydantic and dataclass model implementations, enabling type-safe communication between agents.

Maintained by the team at Legion AI.

Installation

pip install a2a-protocol

Usage

Pydantic v2 Implementation

from a2a_protocol.pydantic_v2 import Message, Part, TextPart, Role

# Create a simple message
message = Message(
    role=Role.user,
    parts=[
        Part(root=TextPart(
            type="text",
            text="Hello, agent!",
            metadata={"source": "user_interface"}
        ))
    ],
    metadata={"session_id": "12345"}
)

Dataclass Implementation

from a2a_protocol.dataclass import Message, TextPart, Role

# Create a simple message using dataclasses
message = Message(
    role=Role.user,
    parts=[
        TextPart(
            type="text",
            text="Hello, agent!",
            metadata={"source": "user_interface"}
        )
    ],
    metadata={"session_id": "12345"}
)

Core Components

Message Types

• TextPart: For text-based messages
• FilePart: For file attachments
• DataPart: For structured data

Task Management

• Task: Represents a task with its status, history, and artifacts
• TaskStatus: Current state of a task (working, completed, failed, etc.)
• TaskState: Enum of possible task states

JSON-RPC Communication

• JSONRPCRequest: Standard request format
• JSONRPCResponse: Standard response format
• SendTaskRequest, GetTaskRequest, CancelTaskRequest: Specific request types

Protocol Workflow

┌──────────────┐            ┌──────────────┐
│              │            │              │
│   Agent A    │◄──────────►│   Agent B    │
│              │    A2A     │              │
└──────────────┘  Protocol  └──────────────┘
       │                            ▲
       │                            │
       │         ┌──────────┐       │
       └────────►│  Tasks   │◄──────┘
                 │          │
                 └──────────┘

Features

• Full type-checked implementation of the A2A protocol
• Both Pydantic v2 and dataclass implementations
• Complete support for:
  • Task creation and management
  • Messaging between agents
  • File and data transfer
  • Status updates and notifications
  • Error handling

Protocol Structure

The A2A protocol enables agents to:

1. Create and manage tasks
2. Send and receive messages
3. Share structured data and files
4. Monitor task status and progress
5. Handle errors and notifications

License

MIT