A real multi-resolution .ico file, not just a renamed PNG

A lot of “favicon generators” just resize your image to 32×32 and slap a .ico extension on a PNG. That works in most modern browsers, but it isn’t actually a valid ICO file, and it means a single low-resolution image gets stretched for every context that expects an icon, from a browser tab to a Windows taskbar shortcut. This tool builds a real Microsoft Icon (.ico) container, the same binary format Windows itself uses, embedding three separately rendered resolutions (16×16, 32×32, 48×48) inside one file so whatever’s displaying it can pick the size that actually looks sharp.

How the .ico file is actually built

Each resolution is rendered independently onto its own canvas at its native pixel size, not scaled down from a single large render, so small sizes like 16×16 get their own crisp pass rather than a blurry downsample. Each canvas is exported as PNG bytes, then packed into the ICO container format directly: a 6-byte header declaring the icon type and image count, followed by one 16-byte directory entry per image describing its dimensions and byte offset, followed by the actual PNG data for each size back to back. Storing PNG data inside an ICO entry (rather than raw uncompressed bitmap data, which is how ICO originally worked in the 1990s) has been supported since Windows Vista and is what every modern favicon needs.

Generate from an image, or generate from initials

Upload mode takes your logo, centres and crops it to a square if it isn’t already one, and renders that square at every required size. Initials mode skips the upload entirely: pick one to three characters, a shape, and two colours, and the tool draws a simple lettermark icon directly on canvas, centring the text and auto-shrinking it to fit if you use three wide characters. This is enough for a placeholder icon or a genuinely minimal brand mark without needing design software.

What’s in the downloaded package

Where the work happens

Library and references

• ICO file format reference for the binary structure this tool writes.
• JSZip bundles every generated file into one downloadable archive.
• Web App Manifest reference for the site.webmanifest fields this tool generates.

Where this gets used

Setting up icons for a brand-new site that only has a square logo, generating a quick placeholder mark for a project that doesn’t have a real logo yet, or replacing an old favicon that only ever had a single blurry 32×32 PNG.