Recommendations
- PageSpeed
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- Avoid a character set in the meta tag
- Avoid bad requests
- Avoid CSS @import
- Avoid CSS expressions (deprecated)
- Avoid document.write
- Avoid Flash on mobile webpages (deprecated)
- Avoid landing page redirects
- Avoid Plugins
- Combine external CSS (deprecated)
- Combine external JavaScript (deprecated)
- Combine images using CSS sprites
- Defer loading of JavaScript (deprecated)
- Defer parsing of JavaScript
- Enable gzip compression
- Enable Keep-Alive
- Improve server response time
- Inline small CSS
- Inline small JavaScript
- Leverage browser caching
- Leverage proxy caching (deprecated)
- Make landing page redirects cacheable (deprecated)
- Minify CSS
- Minify HTML
- Minify JavaScript
- Minimize cookie size (deprecated)
- Minimize DNS lookups (deprecated)
- Minimize redirects
- Minimize request size
- Optimize images
- Optimize the order of styles and scripts
- Parallelize downloads across hostnames (deprecated)
- Prefer asynchronous resources
- Put CSS in the document head
- Remove query strings from static resources
- Remove unused CSS
- Serve resources from a consistent URL
- Serve scaled images
- Serve static content from a cookieless domain
- Specify a cache validator
- Specify a character set early
- Specify a Vary: Accept-Encoding header
- Specify a viewport for mobile browsers
- Specify image dimensions
- Use an application cache
- Use efficient CSS selectors
- YSlow
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- Add Expires headers
- Avoid AlphaImageLoader filter
- Avoid CSS expressions
- Avoid empty src or href
- Avoid HTTP 404 (Not Found) error
- Avoid URL redirects
- Compress components with gzip
- Configure entity tags (ETags)
- Do not scale images in HTML
- Make AJAX cacheable
- Make favicon small and cacheable
- Make fewer HTTP requests
- Make JavaScript and CSS external
- Minify JavaScript and CSS
- Put CSS at the top
- Put JavaScript at bottom
- Reduce cookie size
- Reduce DNS lookups
- Reduce the number of DOM elements
- Remove duplicate JavaScript and CSS
- Use a Content Delivery Network (CDN)
- Use cookie-free domains
- Use GET for AJAX requests
YSlow: Do not scale images in HTML
Overview
Scaling images in HTML can result in unnecessary bandwidth wasted downloading large images.
How does your site score on this recommendation?
Details from Yahoo!
Web page designers sometimes set image dimensions by using the width and height attributes of the HTML image element. Avoid doing this since it can result in images being larger than needed.
Summary
ImagesLow
Moderate
YSlow recommends:
For example, if your page requires image myimg.jpg which has dimensions 240x720 but displays it with dimensions 120x360 using the width and height attributes, then the browser will download an image that is larger than necessary.
Resize your images in an image editor to the actual size you need.