Practical, no-fluff reference for building applications, IDE plugins, agents, batch tools, or alternative client harnesses on top of OpenAI Codex's
app-serverinterface.
This guide distills:
- What
codex app-serveractually is on the wire (transports, handshake, framing). - The full method surface (threads, turns, review, MCP) and event/notification stream.
- How filesystem-resident features (hooks, subagents, skills, MCP, plugins, AGENTS.md) interact with the protocol.
- Where state lives on disk (Codex core state vs. companion state).
- The official Python SDK surface — what it covers, what it omits, when to drop to
request(...).