ExcludeClipboardContentFromMonitorProcessing, Explained

ExcludeClipboardContentFromMonitorProcessing is a registered Windows clipboard format. If an app puts any data in this format alongside its copy, Windows keeps that copy out of clipboard history (Win+V) and doesn't sync it to the user's other devices. Two related formats, CanIncludeInClipboardHistory and CanUploadToCloudClipboard, control history and sync separately. Password managers use them so copied passwords don't pile up in history, and well-behaved clipboard managers check for them too.

The three formats Microsoft documents

Microsoft lists these under "Cloud Clipboard and Clipboard History Formats" on its Clipboard Formats page. They're registered formats, so each app gets the numeric ID by calling RegisterClipboardFormat with the exact name. Every app that registers the same name gets the same ID, which is how the source app and Windows agree.

The flags apply only to the copy they're attached to. They don't turn clipboard history off, and the next ordinary Ctrl+C is recorded as usual.

Apps written against the Windows Runtime API can do the same thing with Clipboard.SetContentWithOptions and a ClipboardContentOptions object, whose IsAllowedInHistory and IsRoamable properties control history and sync.

Clipboard Viewer Ignore

Clipboard Viewer Ignore is an older convention, not part of Microsoft's documentation. A password manager adds a format with this name to tell clipboard viewers and managers to skip the copy. KeePass has an option to use it (on by default since KeePass 2.44), and several third-party clipboard managers check for it. KeePass's FAQ notes that some applications, including some old versions of Microsoft Office, may crash when it's present.

A clipboard monitor that wants to respect password managers should skip a copy when any of these are true:

• ExcludeClipboardContentFromMonitorProcessing is present,
• CanIncludeInClipboardHistory is 0,
• CanUploadToCloudClipboard is 0 (a local-only tool may choose to keep these, since the source only asked not to sync),
• Clipboard Viewer Ignore is present.

What these formats don't do

• They don't hide the data. The text is still on the clipboard in its normal format, and any app in the session can read it with GetClipboardData until something else is copied. Can other apps read everything you copy? covers that side.
• They aren't automatic. The app that copies must set them. A password copied from Notepad, a spreadsheet or a chat window carries no flag and goes into history like any other text.
• They don't replace settings. If a PC should never upload clipboard text, turn off Clipboard history across your devices in Settings > System > Clipboard rather than relying on every app to flag its copies.

Which apps set them and which honour them

1Password and Bitwarden document auto-clear timers for copied passwords. Whether a given version also sets these formats isn't stated on those pages, so test it as shown below. How to stop clipboard managers from saving secrets covers the settings in each manager, and what Edge Drop does with password manager copies lists every format Edge Drop checks.

How to set the formats in your own app (C)

This Win32 example puts a secret on the clipboard with all three documented flags. The flags go on first, so if anything fails, the secret never reaches the clipboard unflagged.

#include <windows.h>
#include <string.h>
#include <wchar.h>

/* Copies data into a movable global block and hands it to the clipboard. */
static BOOL PutData(UINT format, const void *data, SIZE_T size)
{
    HGLOBAL h = GlobalAlloc(GMEM_MOVEABLE, size);
    void *p;
    if (h == NULL) return FALSE;
    p = GlobalLock(h);
    if (p == NULL) { GlobalFree(h); return FALSE; }
    memcpy(p, data, size);
    GlobalUnlock(h);
    if (SetClipboardData(format, h) == NULL) { GlobalFree(h); return FALSE; }
    return TRUE; /* the clipboard owns h now */
}

/* Puts secret text on the clipboard, excluded from history and cloud sync. */
BOOL CopySecretToClipboard(HWND owner, const wchar_t *secret)
{
    const DWORD zero = 0;
    UINT cfExclude = RegisterClipboardFormatW(L"ExcludeClipboardContentFromMonitorProcessing");
    UINT cfHistory = RegisterClipboardFormatW(L"CanIncludeInClipboardHistory");
    UINT cfCloud   = RegisterClipboardFormatW(L"CanUploadToCloudClipboard");
    BOOL ok;

    if (!cfExclude || !cfHistory || !cfCloud) return FALSE;
    if (!OpenClipboard(owner)) return FALSE;
    EmptyClipboard();

    ok = PutData(cfExclude, &zero, sizeof zero)
      && PutData(cfHistory, &zero, sizeof zero)
      && PutData(cfCloud, &zero, sizeof zero)
      && PutData(CF_UNICODETEXT, secret, (wcslen(secret) + 1) * sizeof(wchar_t));

    CloseClipboard();
    return ok;
}

ExcludeClipboardContentFromMonitorProcessing alone is enough for Windows. The two DWORD formats are there for clipboard tools that check only those names. Don't use a private format in the CF_PRIVATEFIRST range for this; Windows and other apps won't recognise it.

How to test whether an app honours the flags

1. Turn on clipboard history (Win+V, then Turn on).
2. In KeePass, with the default clipboard history option on, select an entry and copy its password from the main window.
3. Press Win+V. The password shouldn't appear.
4. Open your clipboard manager. If the password appears there, the manager isn't honouring the flags; exclude the password manager in its settings or use a different tool.
5. Type a test word in Notepad and copy it. It should appear in Win+V, which confirms history is on and only flagged copies are skipped.

Repeat step 2 with your own password manager to see whether it sets the formats. If its copies show up in Win+V, delete them from See more (...) > Delete and rely on its auto-clear timer. How do passwords end up in clipboard history? explains what to do next.

Related reading

• How to Stop Clipboard Managers From Saving Secrets
• How Do Passwords End Up in Clipboard History?
• Can Other Apps Read Everything You Copy?
• How Long Does Windows Keep a Copied Password?

Sources

• Clipboard Formats (Microsoft Learn) — the three cloud clipboard and history formats, their values, and registration.
• Clipboard Class (Microsoft Learn) — SetContentWithOptions.
• ClipboardContentOptions Class (Microsoft Learn) — IsAllowedInHistory and IsRoamable.
• Security (CopyQ documentation) — the formats CopyQ ignores on Windows.
• KeePass 2.44 released (KeePass) — clipboard history option, ClipboardMonitor exclusion, Clipboard Viewer Ignore default.
• KeePass additional FAQ (KeePass) — Ditto exclusion and the Clipboard Viewer Ignore compatibility warning.

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