ACP-WebSocket

Programs on the internet normally talk to each other according to a rigid pattern. One program asks a question, the server answers, and afterward the connection is closed again. A WebSocket does it differently: the line between both sides stays open, and either side may send something at any time. ACP is the abbreviation for Agent Communication Protocol, meaning an agreed-upon set of rules for how AI programs formulate tasks and results among themselves. Combining both, one speaks of ACP-WebSocket: the rules of the protocol run over a permanently open line. The result is a conversation instead of an exchange of letters.

Why agents need an open line

An AI agent is a program that works through a task independently in several steps. It searches for something, checks the result, calls up another tool, and keeps computing. Such tasks sometimes take minutes. With the classic question-and-answer method, the other side would have to check in every two seconds to see if there is anything new. This is called polling, and it wastes computing time and network traffic.

With an open connection, this need to keep asking disappears entirely. The agent reports in on its own as soon as there is an intermediate status. This is exactly what produces the feeling that a chatbot is typing word by word: each piece of text is sent off immediately, instead of waiting for the complete answer. For the user, this significantly shortens the perceived waiting time.

The direction is also important. In a normal connection, only the client is allowed to start speaking. Over a WebSocket, the server can also send a message unprompted, for instance a follow-up question requesting confirmation. An agent tasked with booking a ticket can thus ask for permission in the middle of the process.

From handshake to message loop

The setup begins with a perfectly ordinary web request. In doing so, the client asks for what is called an upgrade, meaning the switch to the WebSocket procedure. If the server agrees, the same line remains in place and is used differently from then on. This process is called a handshake. After that, the connection is neutral: it transports everything that both sides write into it.

This is where ACP comes into play. The protocol defines how a message must be structured so that the other side understands it. Typical are small structured data packets with a field for the message type, an identification number, and the actual content. The identification number ensures that a reply is matched to the correct request. This is necessary because multiple processes can be running simultaneously over an open line.

A common misconception is that ACP-WebSocket is a product of its own. It is merely a combination of content and transport method. The same protocol can also be transmitted via other routes, for example via individual HTTP requests. The WebSocket is the variant for long, lively conversations.

Where this technology is found in products

It is most visible in programming environments with a built-in AI assistant. The editor on the laptop and the model in the cloud maintain a persistent connection over which code suggestions, file changes, and follow-up questions flow. Developer tools such as agent interfaces in the terminal also rely on this pattern.

In companies, it is found wherever multiple agents are meant to work together. One agent does research, a second checks it, a third writes it up. They need a shared channel and a shared vocabulary. In reports about AI platforms, this often appears under keywords such as interoperability or agent ecosystem.

ACP should not be confused with MCP, the Model Context Protocol. MCP primarily governs how a model accesses tools and data sources. ACP is aimed more strongly at communication between independent agents. Both are young standards, and which one will prevail remains open.