ICO and CUR files — Windows icons and cursors — both appear in the SageThumbs format list, and with the extension installed Explorer shows their actual artwork as thumbnails instead of a generic icon about icons. That small change transforms how icon libraries, cursor sets and application resource folders can be managed: instead of opening each 32-pixel file to see which arrow, folder or mascot it contains, you read the whole folder at a glance.
Icons are a special case for thumbnails, because an ICO file is a container holding several images at different sizes and colour depths, and a CUR file applies a similar structure with a hotspot. Windows itself has always been able to display an ICO used as a folder or shortcut icon, but browsing loose ICO and CUR files as documents is exactly where Explorer needed help — and where a shell extension with these formats in its list earns its place.
What the preview shows
An ICO thumbnail represents the file’s artwork, normally using the largest or most suitable contained image for the display size. At Extra large icons you can judge the design properly; at small sizes you see what users will actually see, which is its own kind of test. Cursor files show the pointer graphic, though the hotspot — the exact pixel that clicks — is metadata a thumbnail cannot convey. Animation is the other boundary: an animated cursor (ANI, which is also in the format enumeration) shows as a still representation rather than playing in the folder view.
- ICO: container of multiple sizes; the thumbnail shows the artwork, not the size list.
- CUR: shows the pointer image; hotspot position is not visible in a thumbnail.
- ANI: listed in the official enumeration, shown as a still rather than an animation in Explorer.
- Use Extra large icons for judging design, Small icons for judging real-world legibility.
Setup is the standard installation from SourceForge with an Explorer restart, and neither ICO nor CUR involves GhostScript or any other companion.
Managing icon and cursor collections
Developers keep resource folders where a.ico through z.ico encode an entire product’s visual language, and themers keep cursor sets where the difference between files is a few pixels of styling. Thumbnails make both collections maintainable: duplicates become visible, the odd file from a different set stands out immediately, and renaming passes can be done by looking rather than by opening. Combined with Explorer search, finding every icon that came from one export batch becomes a two-minute job.
| Collection task | Thumbnail value | Still needs |
|---|---|---|
| Auditing an app’s icon set | See all artwork side by side | An icon editor to inspect contained sizes |
| Comparing cursor sets | Spot styling differences at a glance | A cursor tool to check hotspots and animation |
| Finding duplicates | Identical previews in one view | File comparison before deleting |
| Judging small-size legibility | Real-size view in Small icons mode | Nothing — this is the honest test |
Troubleshooting
Because icons are tiny by nature, the most common complaint is not a missing thumbnail but an unreadable one, solved by raising the icon size. If ICO files show a generic image instead, run the standard checks — view mode, Folder Options thumbnail setting, Explorer restart and a cache clear. A single ICO that refuses while others work is usually a malformed or unusually written container; opening and resaving it in an icon editor produces a standard file that previews normally.
Icons at real size: a built-in quality check
Icon design lives or dies at small sizes, and Explorer’s view options turn into a surprisingly honest design review once thumbnails work. Set the folder to Small icons and you see each design at close to the size users will meet in taskbars and lists: artwork that reads clearly there is working; artwork that collapses into a smudge needs simplification, however beautiful it looks at 256 pixels. Step up to Extra large icons and the same folder shows construction detail — alignment, padding, consistency of line weight across a set. Flipping between the two views is a two-second critique that icon designers otherwise need specialist tools to perform. Cursor sets benefit similarly: a set should look like a family, and a folder view exposes the one pointer drawn in a different style instantly. None of this replaces an icon editor for inspecting the exact sizes embedded in a file, but as a first pass over a whole library it is faster than opening files, and it happens in the window where the library already lives.
For developers, one more scenario is worth naming: build output folders. Icon resources generated during a build often land in intermediate directories with generated names, mixed with the other artefacts of the build. When those folders preview properly, confirming that the right icon set was embedded in the right build becomes a visual check instead of a forensic one — open the folder, see the artwork, move on. Small, but builds are made of small checks.
Frequently asked questions
Does SageThumbs show every size inside an ICO file?
No. The thumbnail shows the file’s artwork using a suitable contained image. Inspecting the full list of sizes and depths requires an icon editor.
Are CUR cursor files covered as well as ICO?
Yes. CUR (listed as cursor in the official enumeration) is part of the format coverage, and the pointer graphic is shown as the thumbnail.
Will animated cursors play in Explorer?
No. ANI files are represented as a still image in the folder view; previewing the animation requires a cursor tool.
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