I recently shared my early Emacs experiments with ACP, the Agent Client Protocol now supported by Gemini CLI and Claude Code LLM agents.
While we can already run these agents from Emacs with the likes of vterm, I'm keen to offer an Emacs-native alternative to drive them. To do that, I'm working an a new package: agent-shell (more on this to be shared soon). While this new Emacs agent shell has an opinionated user experience, it uses ACP under the hood. Being a protocol, it's entirely UI-agnostic. For this, I now have an early version available of the acp.el library.
acp.el implements Agent Client Protocol for Emacs lisp as per agentclientprotocol.com. While this library is in its infancy, it's enabling me to carry on with my agent-shell work. acp.el lives as a separate library, is UI-agnostic, and can be used by Emacs package authors to build the their desired ACP-powered agent experience.
You can instantiate an ACP client and send a request as follows:
(setq client (acp-make-client :command "gemini"
:command-params '("--experimental-acp")
:environment-variables (when api-key
(list (format "GEMINI_API_KEY=%s" "your-api-key")))))
(acp-send-request
:client client
:request (acp-make-initialize-request :protocol-version 1)
:on-success (lambda (response)
(message "Initialize success: %s" response))
:on-failure (lambda (error)
(message "Initialize failed: %s" error)))
((protocolVersion . 1)
(authMethods . [((id . oauth-personal)
(name . Log in with Google)
(description . :null))
((id . gemini-api-key)
(name . Use Gemini API key)
(description . Requires setting the `GEMINI_API_KEY` environment variable))
((id . vertex-ai)
(name . Vertex AI)
(description . :null))])
(agentCapabilities (loadSession . :false)
(promptCapabilities (image . t)
(audio . t)
(embeddedContext . t))))
I'm new at using ACP myself, so I've added a special logging buffer to acp.el which enables me to inspect traffic and learn about the exchanges between clients and agents. You can enable logging with:
(setq acp-logging-enabled t)
Look out for the *acp traffic* buffer, which looks a little like this:
If you're keen to experiment with ACP in Emacs lisp and build agent-agnostic packages, take a look at acp.el (now on GitHub). As mentioned, it's early days for this library, but it's a start. Please file issues and feature requests. If you build anything on top of acp.el, lemme know. I'd love to see it in action.
I'm working on two new Emacs packages: acp.el (introduced in this post) and agent-shell (I'll soon share more about that). Please help me make development of these packages sustainable. These packages take time and effort, but also cost me money as I have to pay for LLM tokens throughout testing and development. Please help fund it.
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