app-server.md Codex Docs, 2026-05-14 21:00 UTC → 2026-05-18 22:01 UTC

12Supported transports:12Supported transports:

13 13 

14- `stdio` (`--listen stdio://`, default): newline-delimited JSON (JSONL).14- `stdio` (`--listen stdio://`, default): newline-delimited JSON (JSONL).

15- `websocket` (`--listen ws://IP:PORT`, experimental and unsupported): one JSON-RPC message per WebSocket text frame.15- `websocket` (`--listen ws://IP:PORT`, experimental and unsupported): one

16 JSON-RPC message per WebSocket text frame.

17- Unix socket (`--listen unix://` or `--listen unix://PATH`): WebSocket

18 connections over Codex's default app-server control socket or a custom Unix

19 socket path, using the standard HTTP Upgrade handshake.

16- `off` (`--listen off`): don't expose a local transport.20- `off` (`--listen off`): don't expose a local transport.

17 21 

18When you run with `--listen ws://IP:PORT`, the same listener also serves basic HTTP health probes:22When you run with `--listen ws://IP:PORT`, the same listener also serves basic

23HTTP health probes:

19 24 

20- `GET /readyz` returns `200 OK` once the listener accepts new connections.25- `GET /readyz` returns `200 OK` once the listener accepts new connections.

21- `GET /healthz` returns `200 OK` when the request doesn't include an `Origin` header.26- `GET /healthz` returns `200 OK` when the request doesn't include an `Origin`

27 header.

22- Requests with an `Origin` header are rejected with `403 Forbidden`.28- Requests with an `Origin` header are rejected with `403 Forbidden`.

23 29 

24WebSocket transport is experimental and unsupported. Loopback listeners such as `ws://127.0.0.1:PORT` are appropriate for localhost and SSH port-forwarding workflows. Non-loopback WebSocket listeners currently allow unauthenticated connections by default during rollout, so configure WebSocket auth before exposing one remotely.30WebSocket transport is experimental and unsupported. Local listeners such as

31`ws://127.0.0.1:PORT` are appropriate for localhost and SSH port-forwarding

32workflows. Non-loopback WebSocket listeners currently allow unauthenticated

33connections by default during rollout, so configure WebSocket auth before

34exposing one remotely.

25 35 

26Supported WebSocket auth flags:36Supported WebSocket auth flags:

27 37 

29- `--ws-auth capability-token --ws-token-sha256 HEX`39- `--ws-auth capability-token --ws-token-sha256 HEX`

30- `--ws-auth signed-bearer-token --ws-shared-secret-file /absolute/path`40- `--ws-auth signed-bearer-token --ws-shared-secret-file /absolute/path`

31 41 

32For signed bearer tokens, you can also set `--ws-issuer`, `--ws-audience`, and `--ws-max-clock-skew-seconds`. Clients present the credential as `Authorization: Bearer <token>` during the WebSocket handshake, and app-server enforces auth before JSON-RPC `initialize`.42For signed bearer tokens, you can also set `--ws-issuer`, `--ws-audience`, and

43`--ws-max-clock-skew-seconds`. Clients present the credential as

44`Authorization: Bearer <token>` during the WebSocket handshake, and app-server

45enforces auth before JSON-RPC `initialize`.

33 46 

34Prefer `--ws-token-file` over passing raw bearer tokens on the command line. Use `--ws-token-sha256` only when the client keeps the raw high-entropy token in a separate local secret store; the hash is only a verifier, and clients still need the original token.47Prefer `--ws-token-file` over passing raw bearer tokens on the command line. Use

48`--ws-token-sha256` only when the client keeps the raw high-entropy token in a

49separate local secret store; the hash is only a verifier, and clients still need

50the original token.

35 51 

36In WebSocket mode, app-server uses bounded queues. When request ingress is full, the server rejects new requests with JSON-RPC error code `-32001` and message `"Server overloaded; retry later."` Clients should retry with an exponentially increasing delay and jitter.52In WebSocket mode, app-server uses bounded queues. When request ingress is full,

53the server rejects new requests with JSON-RPC error code `-32001` and message

54`"Server overloaded; retry later."` Clients should retry with an exponentially

55increasing delay and jitter.

37 56 

38## Message schema57## Message schema

39 58 

68 87 

69## Getting started88## Getting started

70 89 

711. Start the server with `codex app-server` (default stdio transport) or `codex app-server --listen ws://127.0.0.1:4500` (experimental WebSocket transport).901. Start the server with `codex app-server` (default stdio transport),

91 `codex app-server --listen ws://127.0.0.1:4500` (TCP WebSocket), or

92 `codex app-server --listen unix://` (default Unix socket).

722. Connect a client over the selected transport, then send `initialize` followed by the `initialized` notification.932. Connect a client over the selected transport, then send `initialize` followed by the `initialized` notification.

733. Start a thread and a turn, then keep reading notifications from the active transport stream.943. Start a thread and a turn, then keep reading notifications from the active transport stream.

74 95 

216 237 

217- `thread/start` - create a new thread; emits `thread/started` and automatically subscribes you to turn/item events for that thread.238- `thread/start` - create a new thread; emits `thread/started` and automatically subscribes you to turn/item events for that thread.

218- `thread/resume` - reopen an existing thread by id so later `turn/start` calls append to it.239- `thread/resume` - reopen an existing thread by id so later `turn/start` calls append to it.

219- `thread/fork` - fork a thread into a new thread id by copying stored history; emits `thread/started` for the new thread.240- `thread/fork` - fork a thread into a new thread id by copying stored history; emits `thread/started` for the new thread. Returned threads include `forkedFromId` when available.

220- `thread/read` - read a stored thread by id without resuming it; set `includeTurns` to return full turn history. Returned `thread` objects include runtime `status`.241- `thread/read` - read a stored thread by id without resuming it; set `includeTurns` to return full turn history. Returned `thread` objects include runtime `status`.

221- `thread/list` - page through stored thread logs; supports cursor-based pagination plus `modelProviders`, `sourceKinds`, `archived`, `cwd`, and `searchTerm` filters. Returned `thread` objects include runtime `status`.242- `thread/list` - page through stored thread logs; supports cursor-based pagination plus `modelProviders`, `sourceKinds`, `archived`, `cwd`, and `searchTerm` filters. Returned `thread` objects include runtime `status`.

222- `thread/turns/list` - page through a stored thread's turn history without resuming it.243- `thread/turns/list` - page through a stored thread's turn history without resuming it. `itemsView` controls whether turn items are omitted, summarized, or fully loaded.

244- `thread/turns/items/list` - reserved for paged turn-item loading; currently returns unsupported.

223- `thread/loaded/list` - list the thread ids currently loaded in memory.245- `thread/loaded/list` - list the thread ids currently loaded in memory.

224- `thread/name/set` - set or update a thread's user-facing name for a loaded thread or a persisted rollout; emits `thread/name/updated`.246- `thread/name/set` - set or update a thread's user-facing name for a loaded thread or a persisted rollout; emits `thread/name/updated`.

225- `thread/goal/set` - set the goal for a loaded thread (experimental; requires `capabilities.experimentalApi`); emits `thread/goal/updated`.247- `thread/goal/set` - set the goal for a loaded thread (experimental; requires `capabilities.experimentalApi`); emits `thread/goal/updated`.

244- `command/exec/resize` - resize a running PTY-backed `command/exec` session.266- `command/exec/resize` - resize a running PTY-backed `command/exec` session.

245- `command/exec/terminate` - stop a running `command/exec` session.267- `command/exec/terminate` - stop a running `command/exec` session.

246- `command/exec/outputDelta` (notify) - emitted for base64-encoded stdout/stderr chunks from a streaming `command/exec` session.268- `command/exec/outputDelta` (notify) - emitted for base64-encoded stdout/stderr chunks from a streaming `command/exec` session.

269- `process/spawn` - start an explicit process session outside Codex's sandbox (experimental; requires `capabilities.experimentalApi`).

270- `process/writeStdin` - write stdin bytes to a running `process/spawn` session or close stdin (experimental).

271- `process/resizePty` - resize a running PTY-backed process session (experimental).

272- `process/kill` - terminate a running process session (experimental).

273- `process/outputDelta` and `process/exited` (notify) - emitted for streaming process output and process exit status (experimental).

247- `model/list` - list available models (set `includeHidden: true` to include entries with `hidden: true`) with effort options, optional `upgrade`, and `inputModalities`.274- `model/list` - list available models (set `includeHidden: true` to include entries with `hidden: true`) with effort options, optional `upgrade`, and `inputModalities`.

248- `modelProvider/capabilities/read` - read provider capability bounds for model/provider combinations (experimental; requires `capabilities.experimentalApi`).275- `modelProvider/capabilities/read` - read provider capability bounds for model/provider combinations (experimental; requires `capabilities.experimentalApi`).

249- `experimentalFeature/list` - list feature flags with lifecycle stage metadata and cursor pagination.276- `experimentalFeature/list` - list feature flags with lifecycle stage metadata and cursor pagination.

250- `experimentalFeature/enablement/set` - patch in-memory runtime enablement for supported feature keys such as `apps` and `plugins`.277- `experimentalFeature/enablement/set` - patch in-memory runtime settings for supported feature keys such as `apps` and `plugins`.

251- `collaborationMode/list` - list collaboration mode presets (experimental, no pagination).278- `collaborationMode/list` - list collaboration mode presets (experimental, no pagination).

252- `skills/list` - list skills for one or more `cwd` values (supports `forceReload` and optional `perCwdExtraUserRoots`).279- `skills/list` - list skills for one or more `cwd` values (supports `forceReload` and optional `perCwdExtraUserRoots`).

253- `skills/changed` (notify) - emitted when watched local skill files change.280- `skills/changed` (notify) - emitted when watched local skill files change.

351## Threads378## Threads

352 379 

353- `thread/read` reads a stored thread without subscribing to it; set `includeTurns` to include turns.380- `thread/read` reads a stored thread without subscribing to it; set `includeTurns` to include turns.

354- `thread/turns/list` pages through a stored thread's turn history without resuming it.381- `thread/turns/list` pages through a stored thread's turn history without

382 resuming it. Use `itemsView` to choose whether turn items are omitted,

383 summarized, or fully loaded.

355- `thread/list` supports cursor pagination plus `modelProviders`, `sourceKinds`, `archived`, `cwd`, and `searchTerm` filtering.384- `thread/list` supports cursor pagination plus `modelProviders`, `sourceKinds`, `archived`, `cwd`, and `searchTerm` filtering.

356- `thread/loaded/list` returns the thread IDs currently in memory.385- `thread/loaded/list` returns the thread IDs currently in memory.

357- `thread/archive` moves the thread's persisted JSONL log into the archived directory.386- `thread/archive` moves the thread's persisted JSONL log into the archived directory.

378{ "id": 10, "result": {407{ "id": 10, "result": {

379 "thread": {408 "thread": {

380 "id": "thr_123",409 "id": "thr_123",

410 "sessionId": "thr_123",

381 "preview": "",411 "preview": "",

382 "ephemeral": false,412 "ephemeral": false,

383 "modelProvider": "openai",413 "modelProvider": "openai",

389 419 

390`serviceName` is optional. Set it when you want app-server to tag thread-level metrics with your integration's service name.420`serviceName` is optional. Set it when you want app-server to tag thread-level metrics with your integration's service name.

391 421 

422`thread.sessionId` identifies the current live session tree root. Root threads

423use their own thread id as the session id; forked threads keep the session id

424of the root they came from. Clients should read the session id from

425`thread.sessionId` instead of deriving it from the thread id.

426 

392To continue a stored session, call `thread/resume` with the `thread.id` you recorded earlier. The response shape matches `thread/start`. You can also pass the same configuration overrides supported by `thread/start`, such as `personality`:427To continue a stored session, call `thread/resume` with the `thread.id` you recorded earlier. The response shape matches `thread/start`. You can also pass the same configuration overrides supported by `thread/start`, such as `personality`:

393 428 

394```json429```json

407 442 

408If you resume with a different model than the one recorded in the rollout, Codex emits a warning and applies a one-time model-switch instruction on the next turn.443If you resume with a different model than the one recorded in the rollout, Codex emits a warning and applies a one-time model-switch instruction on the next turn.

409 444 

445### Manage a thread goal

446 

447`thread/goal/set`, `thread/goal/get`, and `thread/goal/clear` are experimental

448and require `capabilities.experimentalApi = true` plus the `goals` feature. Use

449them for the same persisted goal state surfaced by `/goal` in the TUI.

450 

451```json

452{ "method": "thread/goal/set", "id": 13, "params": {

453 "threadId": "thr_123",

454 "objective": "Finish the migration and keep tests green",

455 "status": "active",

456 "tokenBudget": 40000

457} }

458{ "id": 13, "result": { "goal": {

459 "threadId": "thr_123",

460 "objective": "Finish the migration and keep tests green",

461 "status": "active",

462 "tokenBudget": 40000,

463 "tokensUsed": 0,

464 "timeUsedSeconds": 0

465} } }

466{ "method": "thread/goal/updated", "params": {

467 "threadId": "thr_123",

468 "goal": {

469 "threadId": "thr_123",

470 "objective": "Finish the migration and keep tests green",

471 "status": "active",

472 "tokenBudget": 40000,

473 "tokensUsed": 0,

474 "timeUsedSeconds": 0

475 }

476} }

477```

478 

479Goal objectives must be non-empty and at most 4,000 characters. Supplying a new

480objective replaces the goal and resets usage accounting. Supplying the current

481non-terminal objective, or omitting `objective`, updates status or token budget

482while preserving usage history.

483 

410To branch from a stored session, call `thread/fork` with the `thread.id`. This creates a new thread id and emits a `thread/started` notification for it:484To branch from a stored session, call `thread/fork` with the `thread.id`. This creates a new thread id and emits a `thread/started` notification for it:

411 485 

412```json486```json

413{ "method": "thread/fork", "id": 12, "params": { "threadId": "thr_123" } }487{ "method": "thread/fork", "id": 12, "params": { "threadId": "thr_123" } }

414{ "id": 12, "result": { "thread": { "id": "thr_456" } } }488{ "id": 12, "result": { "thread": { "id": "thr_456", "sessionId": "thr_123", "forkedFromId": "thr_123" } } }

415{ "method": "thread/started", "params": { "thread": { "id": "thr_456" } } }489{ "method": "thread/started", "params": { "thread": { "id": "thr_456" } } }

416```490```

417 491 

435 509 

436Use `thread/turns/list` to page a stored thread's turn history without resuming it. Results default to newest-first so clients can fetch older turns with `nextCursor`. The response also includes `backwardsCursor`; pass it as `cursor` with `sortDirection: "asc"` to fetch turns newer than the first item from the earlier page.510Use `thread/turns/list` to page a stored thread's turn history without resuming it. Results default to newest-first so clients can fetch older turns with `nextCursor`. The response also includes `backwardsCursor`; pass it as `cursor` with `sortDirection: "asc"` to fetch turns newer than the first item from the earlier page.

437 511 

512`itemsView` controls how much turn-item data the response includes:

513 

514- `notLoaded` omits items.

515- `summary` returns summarized item data and is the default when omitted.

516- `full` returns full item data.

517 

438```json518```json

439{ "method": "thread/turns/list", "id": 20, "params": {519{ "method": "thread/turns/list", "id": 20, "params": {

440 "threadId": "thr_123",520 "threadId": "thr_123",

441 "limit": 50,521 "limit": 50,

442 "sortDirection": "desc"522 "sortDirection": "desc",

523 "itemsView": "summary"

443} }524} }

444{ "id": 20, "result": {525{ "id": 20, "result": {

445 "data": [],526 "data": [],

448} }529} }

449```530```

450 531 

532`thread/turns/items/list` is reserved for paged turn-item loading, but the

533current server returns an unsupported-method error.

534 

451### List threads (with pagination & filters)535### List threads (with pagination & filters)

452 536 

453`thread/list` lets you render a history UI. Results default to newest-first by `createdAt`. Filters apply before pagination. Pass any combination of:537`thread/list` lets you render a history UI. Results default to newest-first by `createdAt`. Filters apply before pagination. Pass any combination of:

825 909 

826Use this notification to render the reviewer output in your client.910Use this notification to render the reviewer output in your client.

827 911 

912## Process execution

913 

914`process/*` is an experimental, explicit process-control API. It requires

915`capabilities.experimentalApi = true` and runs outside Codex's sandbox. Use it

916only when your client intentionally exposes local process control without a

917sandbox.

918 

919Start a process with `process/spawn` and provide a `processHandle`, then use

920that handle for stdin, resize, and kill requests. Output streams through

921`process/outputDelta` notifications and completion streams through

922`process/exited`.

923 

924```json

925{ "method": "process/spawn", "id": 48, "params": {

926 "command": ["python3", "-m", "pytest", "-q"],

927 "processHandle": "pytest-1",

928 "cwd": "/Users/me/project",

929 "tty": true

930} }

931{ "id": 48, "result": {} }

932{ "method": "process/outputDelta", "params": {

933 "processHandle": "pytest-1",

934 "stream": "stdout",

935 "deltaBase64": "Li4u"

936} }

937{ "method": "process/exited", "params": {

938 "processHandle": "pytest-1",

939 "exitCode": 0

940} }

941```

942 

943Use `process/writeStdin` with `deltaBase64`, `closeStdin`, or both to send

944input. Use `process/resizePty` for PTY resize events and `process/kill` to

945terminate a running process.

946 

828## Command execution947## Command execution

829 948 

830`command/exec` runs a single command (`argv` array) under the server sandbox without creating a thread.949`command/exec` runs a single command (`argv` array) under the server sandbox without creating a thread.

990- `item/reasoning/summaryPartAdded` - marks a boundary between reasoning summary sections.1109- `item/reasoning/summaryPartAdded` - marks a boundary between reasoning summary sections.

991- `item/reasoning/textDelta` - streams raw reasoning text (when supported by the model).1110- `item/reasoning/textDelta` - streams raw reasoning text (when supported by the model).

992- `item/commandExecution/outputDelta` - streams stdout/stderr for a command; append deltas in order.1111- `item/commandExecution/outputDelta` - streams stdout/stderr for a command; append deltas in order.

993- `item/fileChange/outputDelta` - contains the tool call response of the underlying `apply_patch` tool call.1112- `item/fileChange/outputDelta` - deprecated compatibility notification for legacy `apply_patch` text output. Current app-server versions no longer emit it; use `fileChange` items and `turn/diff/updated` instead.

994 1113 

995## Errors1114## Errors

996 1115 

1050 1169 

1051`dynamicTools` on `thread/start` and the corresponding `item/tool/call` request or response flow are experimental APIs.1170`dynamicTools` on `thread/start` and the corresponding `item/tool/call` request or response flow are experimental APIs.

1052 1171 

1172Dynamic tool names and namespace names must follow Responses API naming

1173constraints. Avoid reserved namespace names used by built-in Codex tools.

1174 

1053When a dynamic tool is invoked during a turn, app-server emits:1175When a dynamic tool is invoked during a turn, app-server emits:

1054 1176 

10551. `item/started` with `item.type = "dynamicToolCall"`, `status = "inProgress"`, plus `tool` and `arguments`.11771. `item/started` with `item.type = "dynamicToolCall"`, `status = "inProgress"`, plus `tool` and `arguments`.

1662- `usedPercent` is current usage within the quota window.1784- `usedPercent` is current usage within the quota window.

1663- `windowDurationMins` is the quota window length.1785- `windowDurationMins` is the quota window length.

1664- `resetsAt` is a Unix timestamp (seconds) for the next reset.1786- `resetsAt` is a Unix timestamp (seconds) for the next reset.

1665- `planType` is included when the backend returns the ChatGPT plan associated with a bucket.1787- `planType` is included when the server returns the ChatGPT plan associated with a bucket.

1666- `credits` is included when the backend returns remaining workspace credit details.1788- `credits` is included when the server returns remaining workspace credit details.

1667- `rateLimitReachedType` identifies the backend-classified limit state when one has been reached.1789- `rateLimitReachedType` identifies the server-classified limit state when one has been reached.

1668 1790 

1669### 7) Notify a workspace owner about a limit1791### 7) Notify a workspace owner about a limit

1670 1792