Mobile first

Make the primary task usable on narrow, zoomed, touch, keyboard, and reduced-motion presentations. Reconsider layout relationships when width changes; do not merely shrink the desktop composition or optimize for the shortest possible page.

Own responsive behavior, not the product

This skill owns viewport-dependent layout, reflow, overflow, touch ergonomics, focus visibility, mobile navigation behavior, and responsive verification.

It does not rewrite the proposition, remove product requirements, invent a mobile-only conversion funnel, or replace the project's visual system. Use landing-page or interface-design first when the underlying information architecture or interface job is wrong.

Choose the mode

• Audit — measure and report without changing files.
• Repair — measure, implement the smallest coherent responsive changes, then compare.
• Build — apply the responsive contract while creating a new interface; there is no before-state baseline.
• Handoff — provide sequenced, independently executable change briefs when the user asks another person or agent to implement.

Infer the mode from the request and state it in one sentence. A request to fix or build authorizes in-scope implementation; do not stop at prompts unless handoff was requested.