What this is
Two protocols ship the agent interop stack in 2026: MCP (Model Context Protocol, Anthropic-originated, 2024) and A2A (Agent-to-Agent, Google-originated, 2025). They are commonly described as competitors but they actually compose: MCP is agent-to-tool, A2A is agent-to-agent. This page is a 2026-05-15 head-to-head explaining the difference and how to use both.
Scope Comparison
| Dimension | MCP | A2A |
|---|---|---|
| Connects | An AI agent to external tools and resources | One AI agent to another AI agent |
| Originator | Anthropic (2024) | Google (2025) |
| Hosted under | Linux Foundation (in process) | Linux Foundation |
| Core primitives | Tools, resources, prompts | Agent cards, tasks, mandates, capabilities |
| Transport | stdio, HTTP, WebSocket | HTTP, gRPC |
| Authentication | OAuth, bearer, mTLS | OAuth 2.0, mTLS, identity assertions |
| Discovery | Server lists, llms.txt pointers | Agent cards (capabilities declared) |
| Cost / payment | Out of scope (use x402 alongside) | Out of scope (use AP2 mandates) |
| Implementations | Hundreds of public servers | Dozens of public agents |
| Adopters | Claude, ChatGPT, Cursor, OpenClaw, many | Google, growing third-party |
How They Compose
- Your agent uses MCP to call your CRM, your database, your brand's MCP server.
- Your agent uses A2A to delegate a subtask to another autonomous agent (a vendor's research agent, a partner's logistics agent).
- The other agent may use its own MCP connections to fulfil the task.
- Settlement and payment between agents flow through x402 or AP2 mandates, not through MCP or A2A.
- The combined stack is: MCP (tools) + A2A (peer agents) + x402 / AP2 (payments).
When to Implement Which
| Goal | Pick |
|---|---|
| Expose your brand's data, catalogue, or APIs to AI agents | MCP server |
| Run an autonomous agent that other agents can call | A2A agent card + endpoint |
| Accept stablecoin payment per API call | x402 (not MCP or A2A) |
| Sign authorised agent-to-agent mandates | AP2 (not MCP or A2A) |
| Local-machine integration (Claude Desktop, Cursor, OpenClaw) | MCP |
| Cross-organisation agent delegation | A2A |
Six Things the Comparison Tells You
- They are not competitors. MCP and A2A are complementary layers in the agent interop stack.
- MCP is winning the tool-integration layer. Hundreds of public servers, native support in Claude, ChatGPT, Cursor, OpenClaw, and others.
- A2A is winning the cross-agent delegation layer. Google's launch + Linux Foundation hosting + growing third-party adoption.
- Payment is a separate concern. Use x402 (for HTTP request-level micropayments) or AP2 (for explicit user-authorised mandates) — neither MCP nor A2A handle payment.
- Most brands will implement MCP first. The MCP server gives immediate value (Claude Desktop, Cursor users can call your data). A2A becomes relevant when you run an autonomous agent that other agents need to invoke.
- The full agentic-commerce stack uses all four. Brand MCP server + brand A2A agent + x402 payment + AP2 mandate = end-to-end agent-to-agent commerce.
How to Pick
Almost everyone needs MCP first. A2A matters when you run an autonomous agent that other organisations' agents call (e.g., you publish an autonomous "research my product" agent for buyers to delegate to). Most brands will need both within 2026-2027 as agentic commerce matures.
Methodology
Protocol detail sourced from Anthropic's MCP documentation, Google's A2A specification, the Linux Foundation hosting announcements, and recent vendor implementations. See A2A vs MCP Agent Communication 2026 for the deeper research write-up.