React and Next.js performance guidance for writing, reviewing, and refactoring production UI code.

React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements.

Debug your apps, find hydration errors, trace your network and more in your react-router app with these devtools

Generate a reusable design.md or DESIGN.md from a live website by deeply inspecting the site with `agent-browser` and `agent-browser eval`, then synthesizing its visual language, layout system, interaction patterns, and content style into a structured markdown design system. Use when given one or more website URLs and asked to analyze a site, reverse-engineer its design, extract its look and feel, write DESIGN.md, create a style guide, or capture a site's UI rules for later AI-assisted design or implementation. Prefer this skill when the goal is documentation rather than rebuilding the page in code. Always use `agent-browser` as the primary browser runtime; if it is missing, help the user install or expose it instead of switching platforms or browser stacks.

Create UI component / widget / reusable piece. Triggers "create component", "new component", "add component", or naming a component (Button, Header, Card).