Browser Use fails on Windows Codex Desktop: failed to start codex app-server (os error 3)

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

• #20130
• #19298
• #20048
• #19423
• #19562

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I can reproduce the same issue on another Windows machine, with the Japanese localized error message.

Environment

• OS: Windows 10.0.26100, x64
• Codex Desktop app package: OpenAI.Codex_26.422.8496.0_x64__2p2nqsd0c76g0
• Codex Desktop Codex.exe product version: 26.422.62136
• Bundled CLI/app-server: 0.126.0-alpha.8
• Browser Use plugin: openai-bundled/browser-use/0.1.0-alpha1

What works

The in-app browser bridge can initialize and read the selected blank tab:

const { setupAtlasRuntime } = await import(
  'C:/Users/<USER>/.codex/plugins/cache/openai-bundled/browser-use/0.1.0-alpha1/scripts/browser-client.mjs'
);

await setupAtlasRuntime({ globals: globalThis, backend: 'iab' });
globalThis.tab = await agent.browser.tabs.selected();

nodeRepl.write(JSON.stringify({
  title: await tab.title(),
  url: await tab.url()
}));

Result:

{"title":"New page","url":"about:blank"}

On about:blank, tab.playwright.domSnapshot() also succeeds and returns an empty snapshot:

{"ok":true,"length":0,"sample":""}

What fails

Both external navigation and nodeRepl.fetch(...) fail immediately:

await tab.goto('https://mail.google.com/mail/u/0/#search/in%3Ainbox+before%3A2026%2F04%2F01', {
  waitUntil: 'domcontentloaded',
  timeout: 30000
});

const res = await nodeRepl.fetch(
  'https://chatgpt.com/backend-api/aura/site_status?site_url=https%3A%2F%2Fmail.google.com'
);

Observed localized error:

Error: failed to start codex app-server: 指定されたパスが見つかりません。 (os error 3)
    at C:\Users\<USER>\AppData\Local\Temp\<TMP>\kernel.js:1675:18
    at handleAuthenticatedFetchResult (C:\Users\<USER>\AppData\Local\Temp\<TMP>\kernel.js:1931:5)
    at handleInputLine (C:\Users\<USER>\AppData\Local\Temp\<TMP>\kernel.js:2008:5)
    at handleInputFrame (C:\Users\<USER>\AppData\Local\Temp\<TMP>\kernel.js:2048:3)

Desktop log evidence

The desktop log shows the app-server transport started and reports version 0.126.0-alpha.8:

info [AppServerConnection] Initializing app-server transport
info [AppServerConnection] Starting app-server connection hostId=local transport=stdio
info [AppServerConnection] Current reported app-server version: currentVersion=0.126.0-alpha.8 hostId=local

The bundled Browser Use plugin is also present/forced:

info [BundledPluginsMarketplace] bundled_plugins_marketplace_sync_started disabledInstalledPluginCount=0 enabledPluginNames=["browser-use","latex-tectonic"] forceInstallPluginNames=["browser-use"]
info [BundledPluginsMarketplace] bundled_plugin_install_requested pluginName=browser-use reason=forced

The native browser-use pipe and IAB tab mapping are created:

info [browser-use-native-pipe-server] browser-use native pipe listening pipePath=\\.\pipe\codex-browser-use\<UUID>
info [browser-use-iab-api] IAB_LIFECYCLE iab createTab mapped page to tab conversationId=<THREAD_ID> pageKey=1:<THREAD_ID> routeKey=1:<THREAD_ID> tabId=1 turnId=<TURN_ID> webContentsId=3
info [browser-use-iab-api] IAB_LIFECYCLE registered debugger listener pageKey=1:<THREAD_ID> routeKey=1:<THREAD_ID> tabId=1 webContentsId=3

Process evidence

The app-server process was observed running:

Name: codex.exe
ExecutablePath: C:\Program Files\WindowsApps\OpenAI.Codex_26.422.8496.0_x64__2p2nqsd0c76g0\app\resources\codex.exe
CommandLine: "...\app\resources\codex.exe" app-server --analytics-default-enabled

Workaround

A separate Playwright MCP browser can open the same external Gmail URL successfully. So the network/page itself is not the blocker; this appears isolated to the Codex in-app browser / Browser Use app-server bridge.

I experience the same error. According to codex debugging itself:

I checked the Browser Use client bundle. There is no normal filesystem path for app-server in browser-client.mjs, and it does not look like something solved by setting PATH.

What the client actually uses on Windows is named pipes:

\\.\pipe\codex-browser-use-iab
\\.\pipe\codex-browser-use
\\.\pipe\codex-browser-use\*
I also checked your machine and these pipes exist:

codex-browser-use\5b2d8b00-7459-42ec-b162-2a4568648804
codex-browser-use\df397824-ffd2-422f-860e-75947e30f318
codex-browser-use\ee81fc03-8c3c-4db5-a5f4-c1e49884acab
codex-browser-use\ffa645a1-46ba-49c8-ace5-bbdd00cc37e2
So the Browser Use client can connect to the Codex/IAB backend. That matches what we saw: tabs.list() works.

The failing message:

failed to start codex app-server: Das System kann den angegebenen Pfad nicht finden. (os error 3)
is coming from the backend after connection, when it tries to start some internal Codex app-server component for navigation/DOM/screenshot work. The exact missing filesystem path is not included in the error returned to me.

The stack I can see points only to the temporary Node REPL kernel:

C:\Users\USERNAME\AppData\Local\Temp\.tmpe2NUJW\kernel.js
That is just the REPL runtime, not the missing app-server path.

So: I don’t think a PATH variable is the fix unless the Codex app-server internally shells out to something by name, but the available error does not expose that. More likely this is a Codex Desktop / Browser Use plugin packaging or runtime-location issue: the backend is reachable, but the app-server binary/folder it expects is missing or not where the backend thinks it is.

I’m also seeing this on Windows Codex Desktop.

The in-app browser opens, but Codex fails when trying to inspect or control it with:
failed to start codex app-server: The system cannot find the path specified. (os error 3)

I can reproduce the same issue on Windows Codex Desktop.

Environment:

• OS: Windows
• Codex Desktop / Windows app
• codex-cli: 0.128.0-alpha.1
• Browser Use plugin: openai-bundled/browser-use/0.1.0-alpha1

What works:

• Browser-in-app can initialize.
• It can see an about:blank tab.
• DOM snapshot on about:blank succeeds.
• The Browser Use plugin file exists:

C:\Users\zhang\.codex\plugins\cache\openai-bundled\browser-use\0.1.0-alpha1\scripts\browser-client.mjs

• Manual app-server startup works:

codex app-server --listen ws://127.0.0.1:0

It listens successfully, for example:

ws://127.0.0.1:60095

• Health checks succeed:

curl.exe -i http://127.0.0.1:60095/healthz
curl.exe -i http://127.0.0.1:60095/readyz

Both return:

HTTP/1.1 200 OK
content-length: 0

What fails:

• Browser-in-app cannot navigate to external websites.
• Navigating to https://example.com/ fails.
• Navigating to https://www.baidu.com/ also fails.
• Error:

failed to start codex app-server: The system cannot find the path specified. (os error 3)

Additional checks:

• codex app-server --help works.
• codex app-server --listen ws://127.0.0.1:0 works manually.
• browser-client.mjs exists and can be read.
• Browser Use is enabled in Codex settings.
• Approval and History permissions are set to Always allow.
• No blocked domains are configured.
• Clearing browsing data and restarting Codex Desktop did not fix it.

This looks like Codex Desktop can run the app-server manually, but the Browser Use / in-app browser integration still fails to auto-start or bind to the app-server when navigating to an external URL.

Cross-linking a local workaround that fixed this same Windows Codex Desktop / Browser Use failed to start codex app-server: ... (os error 3) failure here: https://github.com/openai/codex/issues/19562#issuecomment-4356858649

On my machine, %LOCALAPPDATA%\OpenAI\Codex\bin was expected/on the Desktop path but missing. The helper binaries already existed at:

%LOCALAPPDATA%\Packages\OpenAI.Codex_2p2nqsd0c76g0\LocalCache\Local\OpenAI\Codex\bin

Creating a junction from the expected path to the packaged helper-bin path fixed Browser Use / in-app browser control:

$target = "$env:LOCALAPPDATA\Packages\OpenAI.Codex_2p2nqsd0c76g0\LocalCache\Local\OpenAI\Codex\bin"
$link = "$env:LOCALAPPDATA\OpenAI\Codex\bin"

if (!(Test-Path $target)) { throw "Target not found: $target" }

New-Item -ItemType Directory -Force -Path (Split-Path $link) | Out-Null
if (!(Test-Path $link)) {
    New-Item -ItemType Junction -Path $link -Target $target
}

After adding the junction and retrying in Codex Desktop, Browser Use could attach to the selected in-app browser tab, navigate to external pages, read DOM snapshots, click links, and continue navigating.

This may not cover every Windows Browser Use failure, but it looks relevant when the IAB backend can initialize/list tabs and then navigation/DOM/screenshot work fails with failed to start codex app-server: ... (os error 3).

I can reproduce this on another Windows machine.

Environment:

• OS: Windows 11 Home
• Version: 25H2
• OS build: 26200.8328
• codex-cli: 0.128.0-alpha.1
• Browser Use plugin: openai-bundled/browser-use/0.1.0-alpha1

What works:

• The in-app browser can open and control a local file:// HTML page.
• DOM snapshot, fill, click, and screenshot work on the local page.

What fails:

• Navigating to external HTTPS URLs fails:
• https://www.google.com/
• https://example.com/
• https://x.com/home

Error:
failed to start codex app-server: <Windows message: The specified path was not found> (os error 3)

Additional note:
codex --version also prints:
WARNING: proceeding, even though we could not update PATH: <Windows message: Access is denied> (os error 5)

Updating/repairing Codex, rebooting Windows, and running Codex as administrator did not fix it.

I’m seeing the same issue on Windows Codex Desktop.

Environment:

• OS: Windows
• Codex package path/version: OpenAI.Codex_26.429.8261.0_x64__2p2nqsd0c76g0
• Browser Use plugin: openai-bundled/browser-use/0.1.0-alpha1
• Node installed separately: Node.js 24.15, but this does not appear to affect the issue

What works:

• setupAtlasRuntime({ globals: globalThis, backend: "iab" }) succeeds
• Browser Use can see the in-app browser backend
• agent.browser.tabs.list() returns the blank in-app tab:

[
  {
    "id": "1",
    "url": "about:blank",
    "title": "about:blank"
  }
]
What fails:

tab.goto("https://www.thejournal.ie/")
nodeRepl.fetch("https://chatgpt.com/backend-api/aura/site_status?...")
Both fail with:

failed to start codex app-server: The system cannot find the path specified. (os error 3)
I also tried a full Codex quit/relaunch, but the issue persisted. This appears to be the same app-server bridge failure rather than a site-specific browser problem.

Adding a possibly related root cause from a newer Windows repro.

I saw the same lower-level shape here: Browser Use / policy config reads eventually failed because Codex app-server could not start with os error 3. In my case, the missing path was a stale configured Codex CLI path: CODEX_CLI_PATH and chrome-native-hosts-v2.json paths.codexCliPath pointed to an old hash directory whose codex.exe no longer existed.

Updating those paths to the existing codex.exe and restarting Codex fixed the policy/config read path on that machine. The main diagnostic gap is that the error did not expose the missing configured path, so it looked like a generic app-server failure.

More focused details: #28474

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