favifetch

Based on Vemetric/favicon-api — a TypeScript/Bun favicon API service.
favifetch is the Go library version of the same concept.

A Go library for discovering and fetching website favicons. Automatically finds the best favicon from HTML <link> tags, web app manifests, common fallback locations, and optionally Vemetric's favicon API.

Features

• Smart Discovery — Finds favicons from <link rel="icon">, <link rel="apple-touch-icon">, manifest.json, and common fallback paths (/favicon.ico, /apple-touch-icon.png)
• Quality Ranking — Scores favicons by size, format, and source, returning the best one first
• Format Detection — Detects PNG, JPEG, GIF, ICO, WebP, SVG, BMP via magic bytes
• Image Processing — Resize to any pixel size and convert between PNG, JPG, WebP
• SSRF Protection — Blocks requests to private IPs by default
• Domain Mappings — Maps app package names (e.g. com.pinterest) to canonical domains
• Vemetric API Fallback — Optionally uses Vemetric's favicon.vemetric.com as a last-resort source
• Browser Mode — Selects the regular favicon Chromium would use for a 16px desktop tab from the initial HTML
• Context Support — Full context.Context integration for cancellation and timeouts
• Zero cgo — Pure Go image processing (no Sharp/Node dependency)

Installation

go get github.com/kodehat/favifetch

Quick Start

package main

import (
    "context"
    "fmt"
    "os"

    "github.com/kodehat/favifetch"
)

func main() {
    ctx := context.Background()

    // Fetch a favicon
    result, err := favifetch.Fetch(ctx, "github.com")
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error: %v\n", err)
        os.Exit(1)
    }

    fmt.Printf("Format:  %s\n", result.Format) // png, svg, etc. (implements Stringer)
    fmt.Printf("Size:    %dx%d (%d bytes)\n", result.Width, result.Height, result.Size)
    fmt.Printf("Source:  %s\n", result.Source)
    fmt.Printf("URL:     %s\n", result.SourceURL)

    // result.Data contains the raw image bytes
    // os.WriteFile("favicon."+result.Format, result.Data, 0644)
}

Usage

Basic Fetch

result, err := favifetch.Fetch(ctx, "github.com")
// result.Data → raw image bytes
// result.Format → "svg", "png", "ico", etc.

URLs without a scheme default to https://. Full URLs with paths are also supported:

result, err := favifetch.Fetch(ctx, "https://example.com/blog/post")

With Options

Resize to 128×128 and convert to PNG:

result, err := favifetch.Fetch(ctx, "github.com",
    favifetch.WithSize(128),
    favifetch.WithFormat(favifetch.TargetPNG),
)

Custom timeout and user agent:

result, err := favifetch.Fetch(ctx, "example.com",
    favifetch.WithTimeout(10*time.Second),
    favifetch.WithUserAgent("MyApp/2.0"),
)

Disable Vemetric API fallback and SSRF protection:

result, err := favifetch.Fetch(ctx, "internal.company.com",
    favifetch.WithFallbackAPI(false),
    favifetch.WithBlockPrivateIPs(false),
)

Use a self-hosted Vemetric-compatible API (HTTPS is used; a port is optional):

result, err := favifetch.Fetch(ctx, "example.com",
    favifetch.WithVemetricAPIHost("favicons.example.com:8443"),
)

Chromium Browser Mode

Use browser mode when the selected favicon source should follow Chromium-style regular tab-icon discovery instead of favifetch's quality ranking:

result, err := favifetch.Fetch(ctx, "example.com",
    favifetch.WithMode(favifetch.ModeBrowser),
)

Browser mode considers only HTML <link rel="icon"> candidates and falls back to /favicon.ico only when the page declares none. When WithFallbackAPI(true) (the default) is enabled, it uses the Vemetric API only after those candidates fail, or immediately when the initial HTML request fails (for example, a 403). It honors the final page URL and <base href>, returns the original downloaded bytes, and cannot be combined with WithSize or WithFormat. It does not execute JavaScript or reproduce a browser session's cookies and other runtime state. It always uses a Chromium-like User-Agent; WithUserAgent is ignored in this mode.

Discovery Only

List all discovered favicon sources without fetching any image:

sources, err := favifetch.Discover(ctx, "github.com")
for _, s := range sources {
    fmt.Printf("[%s] score=%d size=%d %s\n", s.Source, s.Score, s.Size, s.URL)
}
// Output:
// [link-tag] score=150 size=0 https://github.githubassets.com/favicons/favicon.svg
// [link-tag] score=70 size=32 https://github.githubassets.com/favicons/favicon.png
// [manifest] score=40 size=192 https://github.githubassets.com/assets/icon-192.png
// [fallback] score=20 https://github.com/apple-touch-icon.png
// [fallback] score=10 https://github.com/favicon.ico
// [fallback-api] score=1 https://favicon.vemetric.com/github.com?size=64

API Reference

Fetch(ctx, url, opts...) (*FaviconResult, error)

Discovers and fetches the best favicon for the given URL.

Discover(ctx, url, opts...) ([]DiscoveredSource, error)

Returns all discovered favicon sources without fetching any image.

Types

type FaviconResult struct {
    Data      []byte          // Raw image bytes
    Format    DetectedFormat  // png, jpg, svg, ico, webp, gif, bmp
    Width     int             // Image width in pixels
    Height    int             // Image height in pixels
    Source    string          // "link-tag", "manifest", "fallback", "fallback-api"
    SourceURL string          // Original URL the favicon was fetched from
    Size      int             // Size of Data in bytes
}

type DiscoveredSource struct {
    URL    string
    Size   int
    Format DetectedFormat
    Source string
    Score  int
}

Options

Option	Default	Description
WithUserAgent(s)	"Favifetch/1.0"	User-Agent header
WithTimeout(d)	5s	Request timeout
WithMaxImageSize(n)	5MB	Max favicon size to accept
WithMaxRedirects(n)	5	Max HTTP redirects
WithBlockPrivateIPs(bool)	true	Block private IP ranges
WithFallbackAPI(bool)	true	Use Vemetric favicon API fallback
WithVemetricAPIHost(host)	favicon.vemetric.com	Set Vemetric-compatible API host (HTTPS)
WithSize(px)	0	Resize to px×px (0 = no resize)
WithFormat(f)	TargetUnspecified	Convert to TargetPNG, TargetJPEG, or TargetWebP
WithHTTPClient(c)	http.DefaultClient	Custom HTTP client
WithPreferredFormats(f...)	(default order)	Set preferred favicon formats in priority order

Favicon Sources & Scoring

The library searches these sources in priority order:

1. HTML <link> tags — <link rel="icon">, <link rel="apple-touch-icon">, <link rel="mask-icon">
2. Web App Manifest — manifest.json icons array
3. Common fallbacks — /apple-touch-icon.png (score 20), /favicon.ico (score 10)
4. Vemetric API — favicon.vemetric.com/<domain>?size=<n> (score 1, optional)

Scoring weights SVG (+100), large sizes (+90 for ≥512px), PNG (+20), WebP (+15), and apple-touch-icon (+10). Mask icons are penalized (−10).

You can customize format priorities with WithPreferredFormats (see below).

Format Preferences

The WithPreferredFormats option lets you control which favicon formats are preferred:

// Prefer SVG, fall back to PNG, then ICO
result, err := favifetch.Fetch(ctx, "example.com",
    favifetch.WithPreferredFormats(favifetch.FormatSVG, favifetch.FormatPNG, favifetch.FormatICO),
)

When preferences are set, sources matching a higher-ranked format get a large score bonus, ensuring they are tried first. Unlisted formats are still tried as a last resort if no preferred format succeeds. Within the same format tier, larger sizes and better sources still win.

// Prefer PNG only — skip SVG entirely unless nothing else works
result, err := favifetch.Fetch(ctx, "example.com",
    favifetch.WithPreferredFormats(favifetch.FormatPNG),
)

When no preferences are set (or nil), the default order is: SVG > PNG > WebP > JPEG > ICO > GIF > BMP.

Error Types

• favifetch.ErrPrivateIP — returned when the target URL resolves to a private IP and BlockPrivateIPs is enabled
• favifetch.errInvalidURL — returned for malformed URLs or unsupported schemes

Credits

Based on Vemetric/favicon-api, a TypeScript/Bun favicon API service by Vemetric.

Built with:

• golang.org/x/net/html — HTML parsing
• golang.org/x/image — Image resampling
• github.com/HugoSmits86/nativewebp — WebP encode/decode
• github.com/srwiley/oksvg + github.com/srwiley/rasterx — SVG rasterization

License

MIT