What is the ANI file format?
The .ani file is a Windows Animated Cursor - the animated counterpart to a static .cur file. Developed by Microsoft and introduced with Windows 95 in 1995, it stores a sequence of cursor frames that the operating system cycles through as a mouse pointer animation. The classic example is the spinning hourglass displayed while Windows processed a task.
Internally, .ani uses the RIFF container format - the same binary container family as .wav audio and .avi video. The file opens with the four bytes RIFF at offset 0, a little-endian file size at offset 4, and the form type ACON (ANImated CONtent) at offset 8. An anih chunk carries the animation header, storing the frame count, step count, and default display rate. Optional rate and seq chunks enable per-frame timing (in 1/60-second jiffies) and non-sequential playback order. The cursor images themselves live in a LIST of icon sub-chunks, each a complete .ico-compatible cursor frame that includes a hotspot coordinate.
Each frame supports color depths from 1-bit monochrome up to 32-bit RGBA with an 8-bit alpha channel, allowing smooth anti-aliased pointer edges. Frame dimensions are typically 32×32 or 48×48 pixels, with support up to 256×256 for high-DPI displays. There is no compression at the container level. The format is Windows-exclusive and has been structurally unchanged since the mid-1990s. To apply a custom .ani pointer, open Windows Pointer Settings in the Control Panel.
Security & safety
RISK: MEDIUMMost .ani files are harmless animated pointers, but the format has a notable security history: a Windows ANI parsing flaw (the 'anih' header) was exploited in the wild (MS05-002 in 2005 and MS07-017/CVE-2007-0038 in 2007) for remote code execution simply by loading a malicious cursor. Those specific bugs are long patched, but the lesson stands - only install cursor packs from reputable sources and keep Windows updated. A cursor from an untrusted ZIP is low-but-nonzero risk on an unpatched system.
Format details
in a nutshellFULL NAMEWindows Animated Cursoraka Animated cursor, RIFF ANI cursor
DEVELOPERMicrosoftsince 1995 (Windows 95 - animated mouse pointers)
CATEGORYSystem Files
MIME TYPEapplication/x-navi-animation
TYPERIFF container of animation frames (binary)
MAGIC BYTES · FILE SIGNATURE
OFFSET
00010203
HEX
52494646
ASCII
RIFF
An ANI is a RIFF file: bytes 0-3 are "RIFF", 4-7 a little-endian size, and bytes 8-11 the form type "ACON" (ANImated CONtent). Frames are stored as a LIST of "icon" chunks, each holding a complete .cur/.ico image. The "anih" chunk carries the animation header.
Programs that open ANI files
Windows5 apps
RealWorld Cursor Editor
Free Open the .ani to preview, edit frames/timing, and export. Free, purpose-built for cursors. 
Windows Pointer Settings
Built-in Settings > Bluetooth & devices > Mouse > Additional mouse settings > Pointers tab > Browse, pick the .ani to assign it. Or right-click the .ani > Install. 
Technical details
deep spec| Container format | RIFF (Resource Interchange File Format) with form type ACON (ANImated CONtent) |
| Magic bytes | 0x52 0x49 0x46 0x46 ("RIFF") at offset 0; "ACON" at offset 8 |
| Byte order | Little-endian throughout |
| Animation header chunk | "anih" chunk stores frame count, step count, default display rate, frame width/height, bit count, and flags |
| Per-frame timing | Optional "rate" chunk: one DWORD per step measured in jiffies (1/60 second each); falls back to the anih header rate if absent |
| Frame sequencing | Optional "seq" chunk allows non-sequential or repeated frame playback order independent of storage order |
| Frame storage structure | LIST chunk of "icon" sub-chunks; each sub-chunk holds a complete CUR/ICO-format cursor image |
| Color depth per frame | 1, 4, 8, 24, or 32 bits per pixel; 32 bpp includes an 8-bit alpha channel for smooth anti-aliased pointer edges |
| Hotspot | Each frame embeds a hotspot (x, y) coordinate marking the pixel that registers as the active click point |
| Frame dimensions | Typically 32x32 or 48x48 px; up to 256x256 px supported for high-DPI displays |
| Compression | None at the RIFF container level; individual frames are stored as uncompressed BMP-based CUR/ICO bitmaps |
| Typical file size | 5 KB to 200 KB depending on frame count and color depth |
| MIME type | application/x-navi-animation; also recognised as image/x-ani |
| Platform support | Windows-only natively; used directly by the Windows cursor subsystem; no built-in support on macOS or Linux |
| Released | 1995 (Windows 95 - animated mouse pointers) |
| Latest version | Stable since the 1990s; format unchanged |
| Specification | learn.microsoft.com |
ANI conversions
Possible
.ANI .CURGUIDE
Yes, you can convert ANI to CUR - open the animated cursor in RealWorld Cursor Editor (free), pick one frame,…
How to convert
.ANI .PNGGUIDE
Yes, you can export frames from an ANI file as PNG images - the quickest way is RealWorld Cursor Editor…
How to convert
.ANI .GIFGUIDE
Yes - use RealWorld Cursor Editor (free) to export the frames directly as an animated GIF, or drop the file…
How to convert
.ANI .JPGGUIDE
You can export one frame from an ANI cursor as a JPG, but the result is a still image with no transparency -…
How to convert
.ANI .ICOGUIDE
Yes, you can export any frame from an ANI file as an ICO - open the file in IcoFX or RealWorld Cursor Editor…
How to convert
Community Q&A
asked by users
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Frequently asked questions
How do I install an ANI animated cursor on Windows?
Right-click the .ani and choose Install, or go to Settings > Mouse > Additional mouse settings > Pointers, select a pointer role, click Browse, and pick the .ani. Click Apply.
How do I open or preview an ANI file?
Use RealWorld Cursor Editor or IcoFX to see the frames and animation, or XnView MP to view it. Windows itself previews it when you Browse for a pointer in mouse settings.
How do I convert an ANI cursor to a GIF?
Extract the frames in RealWorld Cursor Editor or IcoFX and save them as an animated GIF, or use an online ANI-to-GIF converter. This lets you view the animation outside Windows.
What's the difference between an ANI and a CUR file?
A .cur is a single static cursor; an .ani is an animated cursor - a sequence of cursor frames with timing, wrapped in a RIFF/ACON container. ANI is the animated version of CUR.
Can I use an ANI cursor on Mac or Linux?
Not directly - .ani is a Windows-only pointer format. You can view its frames cross-platform (XnView) or convert it to GIF, but assigning it as a system cursor only works on Windows.
How do I make my own animated cursor?
Use RealWorld Cursor Editor (free), IcoFX, or Axialis CursorWorkshop: import a sequence of images or icons, set the hotspot and per-frame timing, and save as .ani.
References
1Microsoft Learn - About Cursors (Win32)learn.microsoft.com
2Microsoft Learn - ANI / RIFF animated cursor structurelearn.microsoft.com
