ADK

In my Agent Protocols - MCP, A2A, A2UI, AG-UI post back in March, I provided a high-level overview of the main agent protocols for tool use (MCP), agent-to-agent communication (A2A), and agent-to-UI interactions (AG-UI and A2UI).

Recently, I had a chance to explore two newer protocols focused on agentic commerce and payments: the Universal Commerce Protocol (UCP) and the Agent Payments Protocol (AP2) . Traditional e-commerce and payment flows assume a human is directly browsing a website and clicking “Buy” on a trusted checkout screen. When an AI agent shops and pays on your behalf, both the commerce workflow and the cryptographic proof of user authorization need a standard language.

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.

In my Agent Protocols - MCP, A2A, A2UI, AG-UI post, I provided a high-level overview of some of the main agent protocols: MCP, A2A, A2UI, and AG-UI. In the Agent-User Interaction Protocol (AG-UI) with Agent Development Kit (ADK) post, I zoomed into the AG-UI protocol and showed how it can be used with Google’s Agent Development Kit (ADK).

In today’s post, I’ll zoom into the A2UI protocol and show how it can be used with Google’s Agent Development Kit (ADK).

In my previous post , I provided a high-level overview of some of the main agent protocols: MCP, A2A, A2UI, and AG-UI. In this post, I will zoom into the AG-UI protocol and show how it can be used with Google’s Agent Development Kit (ADK).

Recap: Agent-User Interaction Protocol (AG-UI)

AG-UI is an open, lightweight, event-based protocol, created by CopilotKit , that standardizes how agent backends connect to agent frontends.