OpenAI open-sources Codex App Server: a JSON-RPC protocol with 120+ client messages powering Codex, Xcode and JetBrains clients
AI Engineer · youtube · 2026-10-09
At AI Engineer World's Fair, Dominik Kundel from OpenAI's Codex DX team presented the Codex App Server — the open-source JSON-RPC protocol that wraps the Codex harness and powers the Codex app, IDE extensions, and third-party clients in Xcode and JetBrains.
- What it is: a protocol layer over the Codex harness, positioned as an alternative to ACP
- Control surface: 120+ client message types, Sign in with ChatGPT (users bring their own subscription), developer instructions layered over the system prompt, dynamic and deferred tools, per-thread model and sandbox settings
- Shipping: distributing the binary, generating bindings, Python SDK, and when to fall back to codex exec
- Demos: a custom inspector showing live events between app and server; Codex running inside Doom with tools that modify the game
Docs at developers.openai.com/codex/app-server; source on GitHub.
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