Agent Client Protocol

Zed introduced Agent Client Protocol in August 2025 under Apache-2.0: JSON-RPC 2.0 over stdio, a wire format between a code editor and a coding agent, modelled on what Language Server Protocol did for language servers. The arithmetic is the argument. N editors against M agents once meant N×M bespoke integrations; with a shared protocol, N+M suffices. The specification page states the problem as integration overhead, limited compatibility, and developer lock-in: "choosing an agent often means accepting their available interfaces."

The protocol has left its creator's orbit. Its site lists Zed Industries and JetBrains at the same level, alongside an ACP Registry, RFDs, and official libraries in Kotlin, Java, Python, Rust, and TypeScript; navigation exposes v1 (Latest) and v2 (Draft). Full support for remote agents over HTTP or WebSocket is still declared a work in progress.

Agent Client Protocol is also where MCP stops: MCP connects an agent to its tools, this one connects a client to an agent, and the two stack. It reuses MCP's JSON representations where possible and defaults to Markdown, adding types for agentic coding UX such as diff display. Block's desktop client Berd reaches the goose runtime through it, and buzz-acp translates between the two protocols inside Buzz.

Franciska Dethlefsen made the open-protocol case economic on 14 May 2026: "your editor is never locked into one provider's pricing decisions." A separate problem is naming. Didier Girard searched the bare acronym in his watch base: twelve results, all about Agentic Commerce Protocol, none about Zed's.