What is CUR? Windows Cursor File Format Explained

How CUR Works

A .cur file is a Windows cursor, and structurally it is almost identical to a Windows icon (.ico). Both use the same on-disk container: a small directory header followed by one or more embedded images, each of which is either a classic device-independent bitmap (DIB) or, on modern Windows, a PNG. The only meaningful difference between an icon and a cursor is a pair of extra fields and a type flag that tells the operating system this resource is meant to be drawn as a pointer rather than as a static icon.

Those extra fields define the hotspot, the single pixel within the image that represents the cursor's actual point of action. When you click, Windows reports the coordinate of the hotspot, not the top-left corner of the bitmap. For an arrow cursor the hotspot sits at the tip of the arrow; for a crosshair it sits at the center. Each image entry in the directory carries its own hotspot X and Y offset, which is exactly where the icon format instead stores color-plane and bit-count information.

Like icons, a cursor file can hold several sizes and color depths in one file, and Windows picks whichever entry best matches the current display scaling and DPI. A well-made cursor might include 32x32 and 48x48 versions so it stays crisp on high-resolution monitors. Transparency is handled either by a legacy AND/XOR mask pair for old bitmap entries or by a genuine alpha channel when the embedded image is a 32-bit bitmap or PNG, which allows soft, anti-aliased edges.

The static .cur format holds a single pointer image. Animated cursors use a separate but related container, the .ani format, which wraps a sequence of cursor frames in a RIFF structure so the pointer can play a short looping animation such as the classic spinning wait cursor. A plain .cur file is always a single, still image with one hotspot per size.

History and Standardization

The cursor format is a Microsoft platform format rather than an open, committee-defined standard. It dates back to the early versions of Windows, where the graphical shell needed a compact way to store the mouse pointer bitmaps together with the click-point information. It has remained backward compatible for decades, which is why cursor files created many Windows versions ago still load correctly today.

Because the cursor and icon formats share their layout, tools and libraries almost always treat them together, distinguishing the two only by the type flag in the header and by the file extension. Windows exposes cursors through its resource system, so applications commonly embed them inside executables and DLLs as well as shipping them as standalone .cur files, and the system offers built-in cursor schemes that users can customize.

The format was never widely adopted outside Windows because it is tied to the Windows pointer subsystem. Other operating systems use their own cursor conventions, such as the X11 cursor formats on Linux. As a result .cur remains a niche, platform-specific format whose sole purpose is customizing the Windows mouse pointer, and it is not used for general image storage.

CUR Compared to ICO and PNG

Against the ICO format, which it closely resembles, the practical difference is intent: an ICO is drawn as a fixed graphic (an application icon, a file-type badge) while a CUR carries a hotspot and is drawn as an interactive pointer. The two are so alike that many editors export both, and a CUR is essentially an ICO with hotspot coordinates in place of the color-plane fields.

Against a plain PNG, a cursor is a container that can hold several PNG or bitmap images at once plus the click-point metadata, whereas a PNG is a single image with no notion of a hotspot or multiple embedded sizes. You cannot use a bare PNG as a Windows cursor without wrapping it in the cursor container so the system knows the hotspot and can select the right size.

For anything other than Windows pointers, .cur is the wrong tool. It is not meant for photographs, web graphics, or general-purpose images, and it lacks the compression efficiency and broad support of formats like PNG or WebP. Its value is narrow and specific: it is the correct and expected way to define a custom mouse cursor on Windows, and nothing else does that job as cleanly.