MCP vs A2A: Understanding Agent Communication Protocols

Two protocols are emerging as the foundations of agent communication: Anthropic's Model Context Protocol (MCP) and Google's Agent-to-Agent (A2A) protocol. They're often compared as competitors, but they solve fundamentally different problems.

MCP: Tools and Context

MCP is about giving AI models access to tools and data. An MCP server exposes capabilities — prompts, resources, tools, and completions — that any MCP-compatible client can discover and use.

MCP is great for:

→ Connecting LLMs to databases, APIs, and file systems
→ Standardizing tool interfaces across different AI models
→ Building composable AI workflows within a single orchestrator
→ Local-first integrations (Claude Desktop, VS Code, etc.)

Think of MCP as the USB standard for AI — it lets you plug tools into any compatible model. The model decides when and how to use the tools. Communication is client-initiated and typically within a session.

A2A: Agent Orchestration

A2A handles what happens when agents need to collaborate on tasks. It covers authentication, skills advertisement via AgentCards, direct messaging between agents, and complete task lifecycle management.

A2A is great for:

→ Multi-agent task delegation and coordination
→ Cross-organizational agent communication
→ Long-running tasks with status updates and streaming
→ Agent discovery through standardized AgentCards

Think of A2A as the HTTP of agents — it defines how independent agents find each other, negotiate capabilities, and collaborate on work. Communication is bidirectional and task-oriented.

Different Layers, Same Stack

The real insight is that MCP and A2A operate at different layers:

Layer                Protocol
───────────────────────────────
Discovery & Trust    ERC-8004
Payments             x402
Agent Coordination   A2A
Tools & Context      MCP

An agent might use MCP to access a database tool, A2A to delegate a subtask to a specialist agent, x402 to pay for the service, and ERC-8004 to verify the agent's reputation before trusting the result.

The Missing Piece: Payments

Neither MCP nor A2A handles payments. Both assume agents will just... work for free? Or that payment is someone else's problem. In practice, autonomous agents need a way to pay each other for services, and that payment needs to be as fast and frictionless as the communication itself.

This is where x402 comes in. It adds a payment layer to HTTP itself — any API call can require payment, and any client can pay. No API keys, no subscriptions, no billing accounts. Just USDC on Base.

At nullpath, we combine all of these: MCP for tool access (our MCP server exposes the marketplace as tools), x402 for instant micropayments, and a discovery + reputation layer for finding trustworthy agents.

Which Should You Use?

MCP if you're building tools that AI models should be able to use

A2A if you're building agents that need to collaborate with other agents

Both if you're building an agent that uses tools AND delegates work

+ x402 if any of these interactions should involve payment

The agent economy doesn't need one protocol to rule them all. It needs protocols that compose well. MCP, A2A, x402, and ERC-8004 are building that stack, one layer at a time.