How do I integrate page experience metrics into the design process?

Short answer: Page experience metrics should be design acceptance criteria, not a post-launch check. The Core Web Vitals thresholds are public: 2.5 seconds for LCP, 200 milliseconds for INP, and 0.1 for CLS. Translate those thresholds into a performance budget during the design phase.

Embedding it in the process

• Define a performance budget: hero image weight, number of font families, and the third-party script list become part of design sign-off.
• Write CLS rules into the design system: reserved space for images, embeds, and ads, fixed heights for late-loading components.
• Standardize interaction feedback for INP: split heavy tasks and never delay the visible response after a click.
• Measure in the lab with Lighthouse on staging; confirm in production with CrUX and RUM field data.
• Set a regression alert: if a release crosses a threshold, design and engineering roll back together.

This keeps the experience debate out of the final week; every design decision arrives with its budget attached.