I use some perf checklists whenever I review a site. Here’s the incomplete list.

Inspired by / forked from Dilip Siva’s perf checklist and AMP project!.

Web Performance Checklist

• Prefer Brotli over gzip / deflate.
• Check caching-headers for all static content (css, js, images, fonts, icons, etc).
• Avoid free DNS from your DNS registrar (there are exceptions, of course).
• Try hosting your whole site in a CDN.
• Reduce the number of DOM elements.

JavaScript

• Use a single resource for loading external JavaScript.

CSS

• Inline critical CSS.
• Use a single resource for (non-critical) CSS loading.
• Only use GPU-accelerated properties.

Images checklist

• Prefer WebP for images over PNG / Jpeg.
• Use a CDN for image-heavy sites.
• Serve small images for mobile users.

Fonts checklist

• Do not use more than 2 external fonts (unless really really necessary on special circumstances).
• Load fonts asynchronously.
• Have plan B if the internet speed is too low!