A2A Protocol Interoperability
A2A Protocol & Agent Interoperability
Reference for the Agent-to-Agent protocol and cross-framework agent communication.
When to use this skill
Activate when the user:
- asks about the A2A protocol or agent-to-agent communication
- wants to publish an Agent Card at
.well-known/agent.json - needs to implement A2A task lifecycle handling
- asks how A2A and MCP work together
- wants cross-framework agent interop (LangGraph <-> CrewAI <-> ADK <-> Claude SDK)
- asks about AAIF, ACP, ANP, or agent protocol governance
- needs to design a multi-vendor agent system
Quick reference
A2A vs MCP
| Aspect | MCP | A2A |
|---|---|---|
| Direction | Vertical (agent -> tools) | Horizontal (agent -> agent) |
| Abstraction | Stateless function calls | Stateful multi-turn tasks |
| Discovery | Server capabilities | Agent Cards at .well-known/agent.json |
| Transport | stdio / Streamable HTTP | JSON-RPC 2.0 over HTTPS + SSE |
| State management | None | 8-state task lifecycle |
Task lifecycle (8 states)
SUBMITTED -> WORKING ----+----> COMPLETED (terminal)
| |----> FAILED (terminal)
| +----> CANCELED (terminal)
|
+----> INPUT_REQUIRED (interrupted)
+----> AUTH_REQUIRED (interrupted)
+----> REJECTED (terminal)Core JSON-RPC operations
| Operation | Method | Purpose |
|---|---|---|
| SendMessage | tasks/send |
Initiate or continue a task |
| SendStreamingMessage | tasks/sendSubscribe |
Real-time SSE updates |
| GetTask | tasks/{id} |
Retrieve current task state |
| CancelTask | tasks/{id}/cancel |
Request cancellation (idempotent) |
Required header: A2A-Version: Major.Minor in all requests.
Governance (2026)
- AAIF (Agentic AI Foundation, Linux Foundation): neutral governance body for A2A and MCP.
- ACP: merged into A2A under AAIF.
- ANP: emerging decentralized peer-to-peer discovery layer above A2A.