What is ACP?

The Agent Client Protocol is an open, newline-delimited JSON-RPC wire format that lets an editor (Zed, WebStorm, IntelliJ, Neovim, Visual Studio via ReSharper) drive a coding agent (Claude Code, Codex, Goose, OpenCode, and 40+ others) over stdio, without either side knowing the other’s implementation. ACP Devtools sits in the middle of that stdio pipe — neither side knows it’s there.

Never seen the wire before? Anatomy of an ACP session walks one real capture frame by frame — handshake, prompt turn, a tool call behind a permission dialog, a cancelled turn — and it’s the same session the playground loads, so you can click along.

Who it’s for

• Agent authors — see exactly what an editor sends, and validate your wire output against the spec.
• Editor / plugin developers — see what the other side sends (WebStorm and Zed disagree on capabilities, _meta, and id format) and test against recorded traffic without burning tokens.
• **Anyone…