ACP (Agent Client Protocol) and MCP (Model Context Protocol) are two complementary open protocols for agentic coding workflows. ACP standardizes the connection between a code editor and an AI coding agent — enabling any ACP agent to run in any ACP editor, similar to how LSP works for language tooling. MCP standardizes the connection between an agent and its tools and data sources (CI systems, databases, etc.). The agent sits between both: ACP handles editor-to-agent communication (sessions, prompts, diffs, permissions), while MCP handles agent-to-tool communication (tool calls, resource reads). They are not competing standards — running both simultaneously is common. ACP is only relevant when an agent runs inside an editor; MCP applies regardless of where the agent runs. Both protocols use JSON-RPC and were inspired by LSP.
