A2E Protocol Architecture
AI Agent
LLM · Codex · Claude
Handshake
Layer 1: Protocol Layer
A2EMessage
Pydantic v2 · Typed
req/resp/event patterns
NDJSON Wire Format
Newline-delimited JSON
Streaming · Versioned
TYPE_MAP Registry
10 capability routes
Extensible
Capability Negotiation
Agent declares caps
Host validates
Dispatches to
Layer 2: Runtime Layer
A2EServer
FastAPI · Uvicorn
Session management
A2EClient
rpc() · events
Capability APIs
PluginRegistry
Dynamic load
Lifecycle · Dispatch
AuditLog
Structured audit
Rotation · JSONL
Transports
HTTP+SSE
Direct
Loads & routes to
Layer 3: Capability Layer — 10 Standard Plugin Namespaces
tools
Named functions
JSON Schema I/O
ToolPlugin
memory
Working tier
Episodic / Semantic
MemoryPlugin
env
RL environments
step · reset · observe
EnvPlugin
proc
Subprocesses
spawn · signal · I/O
ProcPlugin
learn
Feedback
Experience · Adaptation
LearnPlugin
skills
Named execution
Versioned · Sandboxed
SkillPlugin
toolkits
Tool bundles
Shared configuration
ToolkitPlugin
chains
DAG pipelines
Branching · Fan-out
ChainPlugin
mcp
MCP bridge
Proxy tool calls
MCPPlugin
subagents
Multi-agent orchestration
spawn · delegate · merge
SubagentPlugin
Agent/Client
Protocol
Runtime
Capabilities
github.com/a2eprotocol/python-sdk · MIT License
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