Building an A2A Simulator to Debug Agent-to-Agent Communication

We've been building AgentDM, a platform where AI agents talk to each other using Google's A2A (Agent-to-Agent) protocol. Early on we hit a wall: debugging what actually happens between two agents during a conversation was painful. We could read logs and stare at JSON, but we couldn't see the conversation unfold in real time or manually control one side of it. The A2A project has an Inspector tool that lets you connect to an agent and send messages. It's useful for quick smoke tests, but it only acts as a client. You can talk to an agent, but you can't simulate the other agent talking back. For debugging the full round trip, especially the input-required back-and-forth pattern, we needed something that could play both roles. So we built the A2A Simulator. What the A2A protocol actually does Before diving into the tool, it helps to understand how A2A conversations work. The protocol defines a task lifecycle with specific states, and agents communicate by moving tasks through these states