Why this tool is useful
Confirm that a downloaded or generated favicon contains useful browser sizes and that its offsets do not point outside the file or overlap another image payload.
Local File Tools · runs locally
Private ICO Favicon Inspector
Audit an ICO favicon locally and report every embedded size, encoding, bit depth, payload range and structural error without rendering or transmitting the file.
Ready. Your working data stays in this browser.
Files and capture streams stay on this device. Processing uses browser APIs only; nothing is uploaded to YTSave, the media API or a proxy. No server copy is created, stored or left to delete. The file picker is cleared when processing starts, and disposable worker memory is destroyed after completion or cancellation. Preview and generated-output memory is released when you clear the tool or leave the page.
How it works
A bounded binary parser reads ICONDIR and every directory entry, checks ranges and overlap, recognizes PNG or DIB payloads and compares embedded PNG dimensions to the directory.
Practical example
Select favicon.ico before a release and verify that 16, 32 and 48 pixel entries exist, the larger 256 pixel image is PNG encoded and every byte range is structurally valid.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.