Windows: Hook commands cause brief console window flash

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/14828
2. https://github.com/anthropics/claude-code/issues/15572
3. https://github.com/anthropics/claude-code/issues/17230

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
• To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

Update: Findings from Testing

After testing various approaches, discovered that different hook types behave differently:

Key Finding

| Hook Type | Spawn Behavior | node -e Flash? |
|-----------|---------------|------------------|
| statusLine | stdin/stdout piped | No flash ✓ |
| SessionStart | Detached spawn | Flash on Windows ✗ |

Working Workarounds

For statusLine - node -e works without flash:

"command": "node -e \"require(require('os').homedir() + '/.claude/hooks/statusline.js')\""

For SessionStart on Windows - requires mshta trick:

"command": "mshta vbscript:Execute(\"CreateObject(\"\"Wscript.Shell\"\").Run \"\"node \"\"%USERPROFILE%\.claude\hooks\gsd-check-update.js\"\"\"\", 0:close\")"

Request

Adding windowsHide: true to the spawn options for SessionStart (and other detached hooks) would:

1. Eliminate the need for Windows-specific workarounds
2. Allow the same cross-platform command to work everywhere
3. Simplify hook configuration for Windows users

The fact that statusLine already doesn't flash suggests the infrastructure supports it - it may just need to be applied to SessionStart and similar hooks.

Related

Working solution documented in glittercowboy/get-shit-done#144

Anthropic please fix this, it's really annoying and we want to use claude-mem.

Not only do the windows flash, but the main CC window also sometimes crashes when using claude-mem.

I've found a bulletproof solution that completely eliminates the console flash without modifying Claude Code's source. Full research report with technical details: https://claude.ai/public/artifacts/0cd072dd-5e18-4362-9a5b-a184d9dde894

The Root Cause

When Claude Code spawns hooks with child_process.spawn(..., {shell: true}), Node.js invokes cmd.exe via the COMSPEC environment variable. The console window flash happens at CreateProcess time—before any JavaScript executes—which is why windowsHide: true doesn't help.

The Solution

1. Create a GUI subsystem wrapper (no automatic console allocation)
2. Name it cmd.exe and place it in a user directory (e.g., C:\Users\<user>\.claude\cmd.exe)
3. Set COMSPEC to point to this wrapper before launching Claude Code
4. The wrapper spawns the real cmd.exe with CREATE_NO_WINDOW flag and forwards stdio

⚠️ Critical Discovery: The Wrapper MUST Be Named cmd.exe

Node.js uses this regex to detect cmd.exe: /^(?:.*\\)?cmd(?:\.exe)?$/i

If you name it hiddencmd.exe, Node.js will:

• Use -c instead of /d /s /c (breaking cmd.exe syntax)
• Apply wrong quoting/escaping rules
• Fail silently or produce incorrect behavior

Implementation

hiddencmd.cpp (compile as GUI subsystem):

#define UNICODE
#define _UNICODE
#include <windows.h>

int WINAPI wWinMain(HINSTANCE, HINSTANCE, PWSTR, int) {
    // Get real cmd.exe path
    WCHAR realCmd[MAX_PATH];
    GetSystemDirectoryW(realCmd, MAX_PATH);
    wcscat_s(realCmd, MAX_PATH, L"\\cmd.exe");

    // Preserve original command line exactly
    LPWSTR cmdLine = GetCommandLineW();

    // Setup stdio inheritance
    STARTUPINFOW si = { sizeof(si) };
    si.dwFlags = STARTF_USESTDHANDLES;
    si.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
    si.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
    si.hStdError = GetStdHandle(STD_ERROR_HANDLE);

    PROCESS_INFORMATION pi;
    if (!CreateProcessW(realCmd, cmdLine, NULL, NULL, TRUE,
                        CREATE_NO_WINDOW, NULL, NULL, &si, &pi)) {
        return GetLastError();
    }

    WaitForSingleObject(pi.hProcess, INFINITE);
    DWORD exitCode;
    GetExitCodeProcess(pi.hProcess, &exitCode);
    CloseHandle(pi.hProcess);
    CloseHandle(pi.hThread);
    return exitCode;
}

Build (MSVC):

cl /nologo /O2 /W4 /DUNICODE /D_UNICODE hiddencmd.cpp /link /SUBSYSTEM:WINDOWS /OUT:C:\Users\%USERNAME%\.claude\cmd.exe

Build (MinGW-w64):

g++ -O2 -municode -Wl,-subsystem,windows -o C:\Users\%USERNAME%\.claude\cmd.exe hiddencmd.cpp

Launcher integration (set COMSPEC before launching Claude Code):

$env:COMSPEC = "C:\Users\$env:USERNAME\.claude\cmd.exe"
& "C:\path\to\claude.exe" $args

Why This Works

• ✅ Completely eliminates flash (not just reduces)
• ✅ No admin privileges required
• ✅ Survives Claude Code updates (lives in your launcher)
• ✅ Scoped to Claude Code only (other apps unaffected)
• ✅ Preserves stdout/stderr (hooks can output normally)
• ✅ Preserves exit codes

What Doesn't Work

| Approach | Why It Fails |
|----------|--------------|
| windowsHide: true | Window created before option is read |
| NODE_OPTIONS preload | Same—too late |
| nodew.exe | Can't write to stdout |
| Patching cli.js | Reverted on updates, still flashes |
| Job Objects | Can't enforce CREATE_NO_WINDOW on children |
| PATH-based shim | Windows resolves cmd.exe from System32 first |

I've found a bulletproof solution that completely eliminates the console flash without modifying Claude Code's source. Full research report with technical details: https://claude.ai/public/artifacts/0cd072dd-5e18-4362-9a5b-a184d9dde894 ### The Root Cause When Claude Code spawns hooks with child_process.spawn(..., {shell: true}), Node.js invokes cmd.exe via the COMSPEC environment variable. The console window flash happens at CreateProcess time—before any JavaScript executes—which is why windowsHide: true doesn't help. ### The Solution 1. Create a GUI subsystem wrapper (no automatic console allocation) 2. Name it cmd.exe and place it in a user directory (e.g., C:\Users\<user>\.claude\cmd.exe) 3. Set COMSPEC to point to this wrapper before launching Claude Code 4. The wrapper spawns the real cmd.exe with CREATE_NO_WINDOW flag and forwards stdio ### ⚠️ Critical Discovery: The Wrapper MUST Be Named cmd.exe Node.js uses this regex to detect cmd.exe: /^(?:.*\\)?cmd(?:\.exe)?$/i If you name it hiddencmd.exe, Node.js will: Use -c instead of /d /s /c (breaking cmd.exe syntax) Apply wrong quoting/escaping rules Fail silently or produce incorrect behavior ### Implementation hiddencmd.cpp (compile as GUI subsystem): #define UNICODE #define _UNICODE #include <windows.h> int WINAPI wWinMain(HINSTANCE, HINSTANCE, PWSTR, int) { // Get real cmd.exe path WCHAR realCmd[MAX_PATH]; GetSystemDirectoryW(realCmd, MAX_PATH); wcscat_s(realCmd, MAX_PATH, L"\\cmd.exe"); // Preserve original command line exactly LPWSTR cmdLine = GetCommandLineW(); // Setup stdio inheritance STARTUPINFOW si = { sizeof(si) }; si.dwFlags = STARTF_USESTDHANDLES; si.hStdInput = GetStdHandle(STD_INPUT_HANDLE); si.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE); si.hStdError = GetStdHandle(STD_ERROR_HANDLE); PROCESS_INFORMATION pi; if (!CreateProcessW(realCmd, cmdLine, NULL, NULL, TRUE, CREATE_NO_WINDOW, NULL, NULL, &si, &pi)) { return GetLastError(); } WaitForSingleObject(pi.hProcess, INFINITE); DWORD exitCode; GetExitCodeProcess(pi.hProcess, &exitCode); CloseHandle(pi.hProcess); CloseHandle(pi.hThread); return exitCode; } Build (MSVC): cl /nologo /O2 /W4 /DUNICODE /D_UNICODE hiddencmd.cpp /link /SUBSYSTEM:WINDOWS /OUT:C:\Users\%USERNAME%\.claude\cmd.exe Build (MinGW-w64): g++ -O2 -municode -Wl,-subsystem,windows -o C:\Users\%USERNAME%\.claude\cmd.exe hiddencmd.cpp Launcher integration (set COMSPEC before launching Claude Code): $env:COMSPEC = "C:\Users\$env:USERNAME\.claude\cmd.exe" & "C:\path\to\claude.exe" $args ### Why This Works ✅ Completely eliminates flash (not just reduces) ✅ No admin privileges required ✅ Survives Claude Code updates (lives in your launcher) ✅ Scoped to Claude Code only (other apps unaffected) ✅ Preserves stdout/stderr (hooks can output normally) * ✅ Preserves exit codes ### What Doesn't Work Approach Why It Fails windowsHide: true Window created before option is read NODE_OPTIONS preload Same—too late nodew.exe Can't write to stdout Patching cli.js Reverted on updates, still flashes Job Objects Can't enforce CREATE_NO_WINDOW on children PATH-based shim Windows resolves cmd.exe from System32 first

For me, the fix came when they updated claude-mem plugin.

For me, the fix came when they updated claude-mem plugin.

Is it Claude-mem? - That actually sounds right because it happened when I installed Claude-mem. I can't remember what fixed it completely at first, but all I remember is that I put in this prompt to my AI and then it was fixed in 2 mins.
Either way there has to be a way to use Claude-mem because it didn't get that popular without it working.

It also happened before I installed Claude-mem too, it's actually funny how you mentioned that.

Oh, you got it fixed, cool.

Closing for now — inactive for too long. Please open a new issue if this is still relevant.

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.