ICO
ICO icon files for favicon testing
Test ICO uploads, favicon handling, multi-size icons, and MIME detection with signature checks and local image workflows.
Verified . The local inspector checks the ICO header; directory entries and embedded sizes are compared against real ICO inputs, while image baselines come from the PNG generator.
Identify ICO files
- Magic signature
00 00 01 00 (ICO header)- Registered MIME
image/x-icon
ICO is a directory of image entries, each with width, height, and an offset to BMP or PNG data. Browsers pick the best-fit entry, so a valid header does not prove the requested size exists.
Choosing ICO
ICO is the Windows icon container for favicons and app icons, holding multiple sizes and color depths in one file, readable by browsers and OS shell tools. The local generator does not produce ICO files, so validate ICO uploads with the file inspector and use the PNG generator for deterministic image baselines.
Confirm the 00 00 01 00 header instead of trusting the extension.
Test that the expected sizes are actually embedded.
Check PNG-compressed entries separately from BMP entries.
Common test cases
- Favicon upload validation
- Multi-size icon checks
- MIME and signature validation
Invalid and boundary cases
- Directory entry pointing past end of file
- PNG entries in an ICO read as BMP
- Single 16x16 entry used as a large favicon
ICO fixture matrix
This format is generated locally in the browser and does not receive a permanent SEO URL.
Open the local generator