Overview

image/x-icon is the media type traditionally used for Windows ICO files — the favicons shown on browser tabs and bookmarks. Its hallmark is packing icons at several resolutions into a single file.

Details

The ICO container bundles bitmaps (or PNGs) at multiple sizes like 16×16, 32×32, and 48×48 in one file, letting the browser pick a resolution suited to the display context. It is a non-standard registration with the `x-` prefix; the IANA-registered type is `image/vnd.microsoft.icon`, but by long convention image/x-icon is far more common in practice.

Browsers conventionally auto-request `/favicon.ico` at the site root, but modern sites explicitly declare icons in multiple formats and sizes, e.g. `<link rel="icon" href="/favicon.svg" type="image/svg+xml">`. Favicons change rarely, so a long cache lifetime helps, and increasingly sites use a scalable SVG favicon as the default with ICO/PNG as fallbacks.

Syntax

e.g. Content-Type: image/x-icon

File extensions

Notes

• The official IANA type is image/vnd.microsoft.icon, but by browser-compatibility convention image/x-icon still prevails.
• Browsers auto-request `/favicon.ico`, so its absence accumulates 404 logs — provide a minimal icon or point elsewhere via <link>.
• Favicons rarely change, so grant a long max-age via Cache-Control to cut repeat requests.

Related types

Related headers