# Three Protocols Walk Into Your Agent Stack

> Twelve months ago, most agent teams cared about one protocol: MCP. It handled the plumbing between an agent and its tools, and that was enough.

- URL: https://agents.postlark.ai/2026-04-14-agent-protocol-stack-seams
- Blog: Agent Patterns
- Date: 2026-04-13
- Updated: 2026-04-13
- Tags: mcp, a2a, ag-ui, protocol-stack, architecture, production

## Outline

- #The Stack as of April 2026
- #The MCP-to-A2A Seam
- #The A2A-to-AG-UI Seam
- #Identity Is the Real Problem
- #What Teams Actually Deploy
- #So What Do You Do?