llmx/codex-rs/app-server

codex-app-server

codex app-server is the interface Codex uses to power rich interfaces such as the Codex VS Code extension. The message schema is currently unstable, but those who wish to build experimental UIs on top of Codex may find it valuable.

Protocol

Similar to MCP, codex app-server supports bidirectional communication, streaming JSONL over stdio. The protocol is JSON-RPC 2.0, though the "jsonrpc":"2.0" header is omitted.

Message Schema

Currently, you can dump a TypeScript version of the schema using codex app-server generate-ts, or a JSON Schema bundle via codex app-server generate-json-schema. Each output is specific to the version of Codex you used to run the command, so the generated artifacts are guaranteed to match that version.

codex app-server generate-ts --out DIR
codex app-server generate-json-schema --out DIR

Initialization

Clients must send a single initialize request before invoking any other method, then acknowledge with an initialized notification. The server returns the user agent string it will present to upstream services; subsequent requests issued before initialization receive a "Not initialized" error, and repeated initialize calls receive an "Already initialized" error.

Example:

{ "method": "initialize", "id": 0, "params": {
    "clientInfo": { "name": "codex-vscode", "title": "Codex VS Code Extension", "version": "0.1.0" }
} }
{ "id": 0, "result": { "userAgent": "codex-app-server/0.1.0 codex-vscode/0.1.0" } }
{ "method": "initialized" }

Core primitives

We have 3 top level primitives:

• Thread - a conversation between the Codex agent and a user. Each thread contains multiple turns.
• Turn - one turn of the conversation, typically starting with a user message and finishing with an agent message. Each turn contains multiple items.
• Item - represents user inputs and agent outputs as part of the turn, persisted and used as the context for future conversations.

Thread & turn endpoints

The JSON-RPC API exposes dedicated methods for managing Codex conversations. Threads store long-lived conversation metadata, and turns store the per-message exchange (input → Codex output, including streamed items). Use the thread APIs to create, list, or archive sessions, then drive the conversation with turn APIs and notifications.

Quick reference

• thread/start — create a new thread; emits thread/started and auto-subscribes you to turn/item events for that thread.
• thread/resume — reopen an existing thread by id so subsequent turn/start calls append to it.
• thread/list — page through stored rollouts; supports cursor-based pagination and optional modelProviders filtering.
• thread/archive — move a thread’s rollout file into the archived directory; returns {} on success.
• turn/start — add user input to a thread and begin Codex generation; responds with the initial turn object and streams turn/started, item/*, and turn/completed notifications.
• turn/interrupt — request cancellation of an in-flight turn by (thread_id, turn_id); success is an empty {} response and the turn finishes with status: "interrupted".

1) Start or resume a thread

Start a fresh thread when you need a new Codex conversation.

{ "method": "thread/start", "id": 10, "params": {
    // Optionally set config settings. If not specified, will use the user's
    // current config settings.
    "model": "gpt-5-codex",
    "cwd": "/Users/me/project",
    "approvalPolicy": "never",
    "sandbox": "workspaceWrite",
} }
{ "id": 10, "result": {
    "thread": {
        "id": "thr_123",
        "preview": "",
        "modelProvider": "openai",
        "createdAt": 1730910000
    }
} }
{ "method": "thread/started", "params": { "thread": { … } } }

To continue a stored session, call thread/resume with the thread.id you previously recorded. The response shape matches thread/start, and no additional notifications are emitted:

{ "method": "thread/resume", "id": 11, "params": { "threadId": "thr_123" } }
{ "id": 11, "result": { "thread": { "id": "thr_123", … } } }

2) List threads (pagination & filters)

thread/list lets you render a history UI. Pass any combination of:

• cursor — opaque string from a prior response; omit for the first page.
• limit — server defaults to a reasonable page size if unset.
• modelProviders — restrict results to specific providers; unset, null, or an empty array will include all providers.

Example:

{ "method": "thread/list", "id": 20, "params": {
    "cursor": null,
    "limit": 25,
} }
{ "id": 20, "result": {
    "data": [
        { "id": "thr_a", "preview": "Create a TUI", "modelProvider": "openai", "createdAt": 1730831111 },
        { "id": "thr_b", "preview": "Fix tests", "modelProvider": "openai", "createdAt": 1730750000 }
    ],
    "nextCursor": "opaque-token-or-null"
} }

When nextCursor is null, you’ve reached the final page.

3) Archive a thread

Use thread/archive to move the persisted rollout (stored as a JSONL file on disk) into the archived sessions directory.

{ "method": "thread/archive", "id": 21, "params": { "threadId": "thr_b" } }
{ "id": 21, "result": {} }

An archived thread will not appear in future calls to thread/list.

4) Start a turn (send user input)

Turns attach user input (text or images) to a thread and trigger Codex generation. The input field is a list of discriminated unions:

• {"type":"text","text":"Explain this diff"}
• {"type":"image","url":"https://…png"}
• {"type":"localImage","path":"/tmp/screenshot.png"}

You can optionally specify config overrides on the new turn. If specified, these settings become the default for subsequent turns on the same thread.

{ "method": "turn/start", "id": 30, "params": {
    "threadId": "thr_123",
    "input": [ { "type": "text", "text": "Run tests" } ],
    // Below are optional config overrides
    "cwd": "/Users/me/project",
    "approvalPolicy": "unlessTrusted",
    "sandboxPolicy": {
        "mode": "workspaceWrite",
        "writableRoots": ["/Users/me/project"],
        "networkAccess": true
    },
    "model": "gpt-5-codex",
    "effort": "medium",
    "summary": "concise"
} }
{ "id": 30, "result": { "turn": {
    "id": "turn_456",
    "status": "inProgress",
    "items": [],
    "error": null
} } }

5) Interrupt an active turn

You can cancel a running Turn with turn/interrupt.

{ "method": "turn/interrupt", "id": 31, "params": {
    "threadId": "thr_123",
    "turnId": "turn_456"
} }
{ "id": 31, "result": {} }

The server requests cancellations for running subprocesses, then emits a turn/completed event with status: "interrupted". Rely on the turn/completed to know when Codex-side cleanup is done.

Auth endpoints

The JSON-RPC auth/account surface exposes request/response methods plus server-initiated notifications (no id). Use these to determine auth state, start or cancel logins, logout, and inspect ChatGPT rate limits.

Quick reference

• account/read — fetch current account info; optionally refresh tokens.
• account/login/start — begin login (apiKey or chatgpt).
• account/login/completed (notify) — emitted when a login attempt finishes (success or error).
• account/login/cancel — cancel a pending ChatGPT login by loginId.
• account/logout — sign out; triggers account/updated.
• account/updated (notify) — emitted whenever auth mode changes (authMode: apikey, chatgpt, or null).
• account/rateLimits/read — fetch ChatGPT rate limits; updates arrive via account/rateLimits/updated (notify).

1) Check auth state

Request:

{ "method": "account/read", "id": 1, "params": { "refreshToken": false } }

Response examples:

{ "id": 1, "result": { "account": null, "requiresOpenaiAuth": false } } // No OpenAI auth needed (e.g., OSS/local models)
{ "id": 1, "result": { "account": null, "requiresOpenaiAuth": true } }  // OpenAI auth required (typical for OpenAI-hosted models)
{ "id": 1, "result": { "account": { "type": "apiKey" }, "requiresOpenaiAuth": true } }
{ "id": 1, "result": { "account": { "type": "chatgpt", "email": "user@example.com", "planType": "pro" }, "requiresOpenaiAuth": true } }

Field notes:

• refreshToken (bool): set true to force a token refresh.
• requiresOpenaiAuth reflects the active provider; when false, Codex can run without OpenAI credentials.

2) Log in with an API key

1. Send:

   { "method": "account/login/start", "id": 2, "params": { "type": "apiKey", "apiKey": "sk-…" } }
   

2. Expect:

   { "id": 2, "result": { "type": "apiKey" } }
   

3. Notifications:

   { "method": "account/login/completed", "params": { "loginId": null, "success": true, "error": null } }
   { "method": "account/updated", "params": { "authMode": "apikey" } }
   

3) Log in with ChatGPT (browser flow)

1. Start:

   { "method": "account/login/start", "id": 3, "params": { "type": "chatgpt" } }
   { "id": 3, "result": { "type": "chatgpt", "loginId": "<uuid>", "authUrl": "https://chatgpt.com/…&redirect_uri=http%3A%2F%2Flocalhost%3A<port>%2Fauth%2Fcallback" } }
   

2. Open authUrl in a browser; the app-server hosts the local callback.
3. Wait for notifications:

   { "method": "account/login/completed", "params": { "loginId": "<uuid>", "success": true, "error": null } }
   { "method": "account/updated", "params": { "authMode": "chatgpt" } }
   

4) Cancel a ChatGPT login

{ "method": "account/login/cancel", "id": 4, "params": { "loginId": "<uuid>" } }
{ "method": "account/login/completed", "params": { "loginId": "<uuid>", "success": false, "error": "…" } }

5) Logout

{ "method": "account/logout", "id": 5 }
{ "id": 5, "result": {} }
{ "method": "account/updated", "params": { "authMode": null } }

6) Rate limits (ChatGPT)

{ "method": "account/rateLimits/read", "id": 6 }
{ "id": 6, "result": { "rateLimits": { "primary": { "usedPercent": 25, "windowDurationMins": 15, "resetsAt": 1730947200 }, "secondary": null } } }
{ "method": "account/rateLimits/updated", "params": { "rateLimits": { … } } }

Field notes:

• usedPercent is current usage within the OpenAI quota window.
• windowDurationMins is the quota window length.
• resetsAt is a Unix timestamp (seconds) for the next reset.

Dev notes

• codex app-server generate-ts --out <dir> emits v2 types under v2/.
• codex app-server generate-json-schema --out <dir> outputs codex_app_server_protocol.schemas.json.
• See “Authentication and authorization” in the config docs for configuration knobs.