Free ICO sample files
The icon format of Windows and the classic favicon.ico: several sizes of one picture in a single file. Download valid ICO test files, each with a checksum.
- Extension
- .ico
- MIME type
- image/vnd.microsoft.icon
- Kind
- Binary
- Category
- Images
ICO samples
Hand-designed files with realistic content or a specific edge case.
| File | Size | Contents | Download |
|---|---|---|---|
| Sample favicon ICO (4 sizes)sample-favicon.ico | 41.4 KB42,424 bytes | Images: 4 (16 × 16, 32 × 32, 48 × 48, 256 × 256 px) | Download ICO |
What is an ICO file?
An ICO file is a small container. A six-byte header gives the number of images, a directory lists the size and position of each, and the images follow. Windows picks whichever size suits the place where the icon is drawn, and browsers do the same with a favicon.
Each image is stored either as a Windows bitmap without its file header or, since Windows Vista, as a complete PNG. Sizes run up to 256 pixels square; because a size is held in one byte, 256 is written as 0.
How to recognise an ICO file
Software recognises an ICO file by its file signature: fixed bytes at the start of the file, also called magic bytes or a magic number.
| Extension | .ico |
|---|---|
| MIME type | image/vnd.microsoft.icon |
| Also seen as | image/x-icon |
| Origin | Microsoft Windows 1.0; PNG entries since Windows Vista |
| Image encodings | BMP (with a transparency mask) or PNG |
| Largest image | 256 × 256 px |
| Directory entry | 16 bytes for each image |
What to test for
These are the behaviours that most often go wrong when software handles ICO files.
- Two media types are in use: the registered image/vnd.microsoft.icon and the older image/x-icon. Allow-lists should accept both.
- A width or height of 0 in the directory means 256. Code that takes the byte literally reports an image with no size.
- A converter has to choose among several images. Some take the first and some the largest, so a file whose smallest size comes first can yield a 16-pixel result.
Strengths of ICO
- Several sizes in one file, so each context gets a sharp image.
- Read by every browser as a favicon without any markup.
Limitations of ICO
- Limited to 256 × 256 pixels.
- A dated format: PNG and SVG icons are smaller and easier to produce.
Typical uses of ICO test files
- Testing favicon handling in site builders and content systems
- Checking icon parsers and converters
- Verifying which size a tool chooses from a multi-size file
- Testing upload validation that accepts icons
Software that opens ICO
- Every desktop browser, for favicon.ico
- Windows Explorer
- GIMP and ImageMagick
- Pillow and other imaging libraries
Specifications
Related
ICO sample files: questions
- Which sizes does the sample icon contain?
- Four: 16, 32, 48 and 256 pixels square. The three small sizes are 32-bit bitmaps and the largest is an embedded PNG.
- Can I use the sample as a favicon?
- Yes. Serve it as /favicon.ico, or point a link element with rel="icon" at it, to check that your site or framework delivers the file with a suitable content type.
- What is the MIME type of an ICO file?
- The MIME type is image/vnd.microsoft.icon. You will also meet image/x-icon in practice. The file extension is .ico.
- Is a sample ICO file the same as a dummy or example ICO file?
- Yes. Sample, test, dummy and example ICO files are different names for the same thing: an ICO file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy ICO file.