ACP — Communication Protocol Between Agents

Imagine two coworkers who speak different languages—one uses emails, the other uses sticky notes. They’ll never get anything done unless they agree on a common way to pass messages. That’s exactly what ACP does for AI agents.

What Is ACP?

ACP stands for Agent Communication Protocol. It’s a set of rules that lets two AI agents (or an agent and a tool) talk to each other in a clear, structured way—like a universal translator for machines. Instead of each agent guessing what the other means, they follow a shared “language” of requests and replies.

Think of it as the handshake before a conversation. One agent says, “I need this data,” and the other replies, “Here you go, in this exact format.” No confusion, no lost context.

Why Do We Need It?

Without ACP, every agent would need custom code to understand every other agent. That’s like writing a new dictionary for every pair of friends. ACP solves this by creating one standard that everyone can use.

For example, in Hermes Agent, you might have:

• A planner agent that decides what to do.
• A worker agent that actually does the task.
• A memory agent that stores past results.

ACP lets them pass messages back and forth without you writing glue code for each pair.

How Does It Work in Practice?

Here’s a simple example. Suppose you ask Hermes to “book a meeting and send a summary.” The planner agent sends a message to the calendar agent:

{
  "type": "request",
  "action": "create_event",
  "params": {
    "title": "Project Sync",
    "time": "2025-05-01T10:00:00Z"
  }
}

The calendar agent replies:

{
  "type": "response",
  "status": "success",
  "data": {
    "event_id": "12345"
  }
}

Now the planner knows the event is created. It can then send another message to the email agent with the event ID. No one is confused.

Key Rules of ACP

1. Every message has a type – either request or response.
2. Every request has an action – like create_event or get_weather.
3. Every response has a status – success or error.
4. Data is structured – using JSON, so it’s easy to read and parse.

That’s it. Simple, but powerful.

A Real-World Analogy

Think of ordering food at a restaurant. You (the user) give your order to the waiter (planner agent). The waiter writes it on a ticket (ACP message) and hands it to the chef (worker agent). The chef cooks the dish and puts the plate in the pass (response). The waiter picks it up and brings it to you. Everyone knows the ticket format, so the kitchen runs smoothly.

Summary and Practical Tip

ACP is the invisible glue that lets AI agents cooperate without chaos. It’s all about clear, structured messages—nothing more, nothing less.

Practical tip: When building your own agents in Hermes, always define your message types and actions before writing the logic. Start with a simple JSON template like the one above, and test with two agents first. Once that works, add more. You’ll save hours of debugging later.

Now go talk to your agents—they’ll understand each other just fine.