Note: I'll try to include the most relevant metrics on the Part 4 of my Front End Developer Automation series. If you'd like to collaborate, please let me know @papaponmx.

For me the depending on the topic, some of those are:

• <meta> tags presence and confirm that they include relevant content.
• Validate all html tags.
• First meaningful paint.
• Number, size and latency of initial requests and their relevance.
• Font sizes and images size on mobile devices.
• Color contrast ratio.
• Can I traverse the app just with the keyboard?

What are yours?