A2A

In my Agent Protocols - MCP, A2A, A2UI, AG-UI post, I provided a high-level overview of the main agent protocols, including the Agent2Agent (A2A) Protocol. When building an A2A server, you need an easy way to test that its agent card is published properly and that it responds to messages as expected.

Traditionally, you either had to write a custom client script using the A2A SDK or clone and run the web-based A2A Inspector. Recently, the A2A project released the official A2A CLI (a2a) tool, which makes testing A2A agents as simple as running a single terminal command. Even better, it includes a built-in server mode to spin up test agents or wrap existing scripts as A2A servers.

It feels like every other month, there is a new agent protocol and it’s getting hard to keep track of which protocol is used when. Recently, I looked into some of the main agent protocols and in this post, I will provide a high-level overview of MCP, A2A, A2UI, and AG-UI.

TLDR

If you’re too busy or too impatient to read the whole blog post, here’s a summary of the protocols along with links to samples in my repository: