Agent Client Protocol (ACP)

protocol agent open-source

This item was not updated in last three versions of the Radar. Should it have appeared in one of the more recent editions, there is a good chance it remains pertinent. However, if the item dates back further, its relevance may have diminished and our current evaluation could vary. Regrettably, our capacity to consistently revisit items from past Radar editions is limited.

Mar 2026

Trial

The Agent Client Protocol (ACP) is an open standard that defines how code editors communicate with AI coding agent — the same problem that LSP solved for language intelligence. Created by Zed Industries at Google's request, co-developed with JetBrains, and now supported by 30+ agent including Gemini CLI, Claude Code, GitHub Copilot CLI, Goose, and Kiro.

The Problem It Solves

Without ACP, every new agent-editor combination requires custom integration work. Agents must implement editor-specific APIs, and editors must build bespoke integrations for each agent. This is the N × M problem — the same one that LSP (Language Server Protocol) solved for language intelligence a decade ago.

ACP reduces this to N + M: agent implement one protocol, editors adopt one protocol, and everything works together.

How It Works

ACP uses JSON-RPC 2.0 over stdio (local agent) or HTTP/WebSocket (remote agent) to relay user requests to agent and render responses. The protocol defines a minimal set of endpoints:

Endpoint	Purpose
`session/new`	Create a new agent session
`session/prompt`	Send a user message to the agent
`session/load`	Resume a previous session
Permission requests	Agent asks the editor for approval before tool execution
File operations	Agent reads/writes files through the editor

Where It Fits in the Stack

ACP, MCP, and A2A operate at different layers and are complementary:

Editor <──ACP──> Agent <──MCP──> Tools/Data
                   │
                  A2A
                   │
                 Other Agents

ACP standardises editor-to-agent communication (this entry)
MCP standardises agent-to-tool communication
A2A standardises agent-to-agent communication

Editor Support

Editor	Status
Zed	Native (first-party)
JetBrains IDEs	Integrated via AI Assistant plugin; co-developed with Zed
Neovim	Via CodeCompanion and avante.nvim plugins
Emacs	Via agent-shell plugin
Obsidian	Via community plugin
VS Code	Not supported — open issue under discussion, but no commitment from Microsoft

The VS Code gap is significant — it holds ~70% editor market share. However, Microsoft is adopting ACP on the agent side (Copilot CLI) while pursuing its own approach (AgentHQ) on the editor side.

Agent Support

30+ agent are listed in the ACP Registry (launched January 2026):

Agent	Provider	Notes
Gemini CLI	Google	Reference implementation
GitHub Copilot CLI	Microsoft/GitHub	GA since February 2026
Claude Code	Anthropic	Via `claude-agent-acp` adapter (not native)
Goose	Block	Native ACP
Kiro CLI	AWS	Native ACP
Codex CLI	OpenAI	Via adapter
Mistral Vibe	Mistral	Native ACP
Kimi CLI	Moonshot AI	Native ACP
Cline	Community	Supported
Qwen Code	Alibaba	Supported

Why It's in Trial

For Trial:

JetBrains co-developing the protocol and integrating across their entire IDE lineup — the second-largest IDE vendor after Microsoft
Google initiated the project and contributed the reference implementation (Gemini CLI)
GitHub Copilot CLI reached GA with ACP support in February 2026
SDKs in 4 languages (Python, Rust, TypeScript, Kotlin)
30+ agent in the registry, including offerings from Google, Microsoft, Anthropic, AWS, Block, and OpenAI

Why not Adopt:

Pre-1.0 spec (v0.11.3 as of March 2026) — still evolving, expect breaking changes
VS Code holdout — the dominant editor hasn't committed, limiting reach
Remote agent support incomplete — cloud/remote deployment scenarios still being worked on
Claude Code requires an adapter, not native support — Zed maintains the bridge
No standardised permission model — permission handling is inconsistent across implementations

Key Characteristics

Property	Value
Created by	Zed Industries (at Google's request)
Co-developed with	JetBrains (since October 2025)
Announced	August 27, 2025
Current version	v0.11.3 (March 18, 2026)
License	Apache 2.0
Transport	JSON-RPC 2.0 over stdio / HTTP / WebSocket
Registry	agentclientprotocol.com
GitHub	agentclientprotocol/agent-client-protocol