Is Embedding Images in CSS or HTML Using Data/Base64 a Good Practice?

Embedding Images in CSS or HTML Using Data/Base64

To optimize server requests, some developers embed small images (PNG & SVG) as BASE64 strings directly into CSS files. This technique is intended to save HTTP requests while maintaining image visibility.

Is data: URL embedding a good practice?

Embedding images with data: URLs can be beneficial in certain circumstances:

• For very small CSS images (less than 32k after base64 encoding)
• When used as CSS sprites (combining multiple images into one)
• When IE compatibility is not a concern

Reasons to avoid data: URL embedding:

Despite its potential benefits, data: URL embedding has some notable drawbacks:

• Browser compatibility: IE6 and IE7 do not support data: URLs. IE8 supports them only for resources up to 32k in size.
• Page bloat: Data: URLs increase the size of HTML or CSS files by encoding images as text strings.
• Uncacheable images: Embedded images become uncacheable, as they are loaded every time the containing page or style sheet is accessed.
• Performance overhead: Base64 encoding increases image size by 33%. This can strain server resources, especially when serving gzipped content.

Embedding CSS and JS with data: URLs

While it may seem logical to embed CSS and JavaScript using data: URLs for the same reasons as images, this is generally not recommended. CSS and JavaScript files are typically much larger than CSS images, making data: URL embedding impractical and resource-intensive.

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