Agent Skills: UI Page Standards

UI Page Standards

Use when creating a new page.tsx, route segment, or auditing existing pages.

Page Metadata (MANDATORY for New Pages)

Required Exports

• Every new page.tsx MUST export metadata (static) or generateMetadata (dynamic)
• NEVER ship a page with default/empty Next.js metadata

Required Fields

| Field | Requirement | |-------|------------| | title | Unique, descriptive. Format: "Page Title | Site Name" or per project template | | description | 150-160 characters, compelling, includes primary keyword | | openGraph.title | Match or extend the page title | | openGraph.description | Match or extend the page description | | openGraph.images | At least one image, 1200x630px (standard) or 1200x1200px (square) | | openGraph.type | 'website', 'article', or appropriate type | | twitter.card | 'summary_large_image' | | twitter.title | Match the page title | | twitter.description | Match the page description | | twitter.images | Match the link preview image |

Link Preview Image

Every page needs a preview image for social sharing (Slack, Twitter, iMessage, LinkedIn).

• Check if the project already has a default preview image (/app/opengraph-image.png or similar)
• If a project default exists, reference it
• If a route-specific image makes sense, add opengraph-image.png (static) or opengraph-image.tsx (dynamic) in the route segment
• If no image exists and you don't know what to use: ASK THE USER. Do not skip it, do not use a placeholder.
• Standard dimensions: 1200x630px

Static vs Dynamic

• Static page with known content: use metadata export object
• Dynamic route with params (e.g., [slug]): use generateMetadata({ params }) function

New Page Checklist

When creating a new page, the builder MUST also create or verify:

| File | Purpose | When to skip | |------|---------|-------------| | loading.tsx | Loading skeleton matching the page layout | Static pages with no data fetching | | error.tsx | User-friendly error boundary with retry action | Never -- every page needs error handling | | Navigation link | Page must be reachable from existing UI | Only if page is accessed via direct URL (e.g., callback pages) | | Metadata | Title, description, openGraph, twitter, preview image | Never |

Rules:

• loading.tsx skeleton MUST mirror the page's layout structure (not a generic spinner)
• error.tsx MUST show a user-friendly message with a "Try Again" button that calls reset()
• Navigation: check if the page should appear in the site's primary nav, sidebar, or footer. If unsure, ASK THE USER.
• For nested routes: check if breadcrumbs are appropriate

Component States

Every data-driven component MUST handle three states:

| State | What to show | Anti-pattern | |-------|-------------|-------------| | Loading | Skeleton matching final layout, OR spinner with context | Blank screen, no indicator | | Empty | Friendly message explaining no data + action (e.g., "No posts yet. Create your first post.") | Blank screen, empty table with just headers | | Error | User-friendly message + retry action. NEVER show raw error messages or stack traces to users. | White screen, console.error only, generic "Something went wrong" with no action |

Rules:

• Loading skeletons must match the final layout shape (same heights, widths, spacing)
• Empty states must have an action when possible (create, import, change filters)
• Error states must offer retry. For persistent errors, offer an alternative path.
• Use Suspense boundaries at appropriate levels (page-level for main content, component-level for independent sections)
• If using React Server Components: errors in server components bubble to nearest error.tsx. The builder must ensure one exists.

Form Completeness

Every form MUST have:

| Requirement | Implementation | Anti-pattern | |------------|----------------|-------------| | Client-side validation | Required fields marked, format validation (email, phone, URL), min/max length. Use Zod, react-hook-form, or HTML5 validation per project conventions. | No validation, console.log errors | | Visible error messages | Error text shown next to the field that has the error. Use aria-describedby for accessibility. | Errors only in console, alert() boxes, errors at top with no field association | | Submit loading state | Button shows loading indicator during submission. Button text preserved (not replaced with spinner only). | No feedback during submission | | Double-submit prevention | Disable submit button while request is in-flight. | User clicks 3 times, 3 records created | | Success feedback | Toast notification, inline success message, or redirect. User must KNOW it worked. | Form submits, nothing visible changes | | Unsaved changes warning | For important forms (multi-step, long forms): warn before navigation. Not needed for simple search/filter forms. | User fills 10 fields, accidentally navigates away |

Rules:

• Validation messages must be specific ("Email must include @") not generic ("Invalid input")
• Server-side validation is ALSO required for security -- client-side is for UX only
• For server actions: use useFormStatus() for pending state, useFormState() for error handling
• For API routes: validate input with Zod or similar, return structured errors
• If you don't know what validation rules to apply: ASK THE USER.

Mobile-First

Every UI change must work on mobile:

| Rule | Specifics | |------|-----------| | Touch targets | Minimum 44x44px for interactive elements (buttons, links, inputs) | | No horizontal overflow | Test at 320px width minimum. No content should require horizontal scrolling. | | Readable text | Minimum 16px for body text on mobile. No text below 14px. | | Navigation | Must be usable on mobile (hamburger menu, bottom nav, or collapsible sidebar) | | Forms on mobile | Inputs must be full-width or near full-width. Use appropriate input types (type="email", type="tel") for mobile keyboards. | | Images | Must scale properly. Use sizes prop for responsive images. | | Spacing | Reduce section spacing on mobile (see typography-spacing skill mobile column). |

Rules:

• The builder's Design Intent MUST include a "Mobile Approach" section stating how the layout adapts
• If a design looks good on desktop but would clearly break on mobile, the builder must address it proactively

Structured Data and SEO

When creating pages that represent entities (articles, products, FAQs, events, organizations):

| Page Type | JSON-LD Schema | When to add | |-----------|---------------|-------------| | Article/Blog post | Article or BlogPosting | Always for content pages | | Product | Product with offers | Always for e-commerce | | FAQ | FAQPage with questions | When page has Q&A format | | Organization/About | Organization | Homepage or about page | | Event | Event | Event listing pages | | Breadcrumb | BreadcrumbList | Nested pages with breadcrumb UI |

Rules:

• JSON-LD goes in a <script type="application/ld+json"> tag
• In Next.js App Router: use the metadata export or generateMetadata to include JSON-LD
• Canonical URLs: every page should have a canonical URL. Use metadata.alternates.canonical
• If you don't know the schema type for a page: ASK THE USER.
• This is NOT required for utility pages (settings, login, admin dashboards, etc.)

API Route Patterns

When creating or modifying Next.js API routes (route.ts files):

| Requirement | Implementation | |------------|----------------| | Input validation | Validate request body/params with Zod or similar. Return 400 with specific error messages. | | Consistent error format | All errors return: { error: string, details?: object }. Never return raw error objects or stack traces. | | Proper HTTP status codes | 200 success, 201 created, 400 bad request, 401 unauthorized, 403 forbidden, 404 not found, 500 internal error. | | Error handling | Wrap handler in try/catch. Log server errors (don't swallow). Return user-safe error messages. | | Type safety | Request and response types defined. Use Zod .parse() or .safeParse() for runtime validation. |

Rules:

• Never expose internal error messages to clients (security risk)
• For authenticated routes: check auth FIRST, before any other logic
• For mutations: consider idempotency (especially for payment-related routes)

Site Infrastructure

Check that these exist when working on a new Next.js project:

| File | Purpose | Required? | |------|---------|-----------| | app/sitemap.ts or app/sitemap.xml | Search engine discovery | Yes for public sites | | app/robots.ts or public/robots.txt | Crawler instructions | Yes for public sites | | app/favicon.ico or app/icon.tsx | Browser tab icon | Yes always | | app/apple-icon.png | iOS home screen icon | Recommended | | app/manifest.ts or public/manifest.json | PWA manifest | Only if PWA | | app/opengraph-image.tsx or default preview image | Default link preview | Yes |

Rules:

• Don't create these automatically -- ASK if the project needs them
• For existing projects: check what exists and only flag what's missing
• This is a ONE-TIME check, not a per-page check

Dark Mode / Theme Considerations

When implementing or touching theme/color-related code:

| Issue | Prevention | |-------|-----------| | Flash of wrong theme (FOUC) | Use <script> in <head> to set theme class BEFORE React hydrates. Or use next-themes. | | Images that need dark variants | Use <picture> with prefers-color-scheme media query, or CSS filter: invert() for simple icons | | Hardcoded colors | All colors must come from design tokens / CSS custom properties that change with theme | | Third-party embeds | Some embeds don't respect dark mode. Note as known limitation. |

Rules:

• Only applies when the project HAS dark mode or the task is adding dark mode
• If adding dark mode: use next-themes or a similar battle-tested solution
• Test both themes before declaring done