harden

SKILL.md

Strengthen interfaces against edge cases, errors, internationalization issues, and real-world usage scenarios that break idealized designs.

Assess Hardening Needs

Identify weaknesses and edge cases:

Test with extreme inputs:

Very long text (names, descriptions, titles)

Very short text (empty, single character)

Special characters (emoji, RTL text, accents)

Large numbers (millions, billions)

Many items (1000+ list items, 50+ options)

No data (empty states)

Test error scenarios:

Network failures (offline, slow, timeout)

API errors (400, 401, 403, 404, 500)

Validation errors

Permission errors

Rate limiting

Concurrent operations

Test internationalization:

Long translations (German is often 30% longer than English)

RTL languages (Arabic, Hebrew)

Character sets (Chinese, Japanese, Korean, emoji)

Date/time formats

Number formats (1,000 vs 1.000)

Currency symbols

CRITICAL: Designs that only work with perfect data aren't production-ready. Harden against reality.

Hardening Dimensions

Systematically improve resilience:

Text Overflow & Wrapping

Long text handling:

/* Single line with ellipsis */
.truncate {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* Multi-line with clamp */
.line-clamp {
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

/* Allow wrapping */
.wrap {
  word-wrap: break-word;
  overflow-wrap: break-word;
  hyphens: auto;
}

Flex/Grid overflow:

/* Prevent flex items from overflowing */
.flex-item {
  min-width: 0; /* Allow shrinking below content size */
  overflow: hidden;
}

/* Prevent grid items from overflowing */
.grid-item {
  min-width: 0;
  min-height: 0;
}

Responsive text sizing:

Use clamp() for fluid typography

Set minimum readable sizes (14px on mobile)

Test text scaling (zoom to 200%)

Ensure containers expand with text

Internationalization (i18n)

Text expansion:

Add 30-40% space budget for translations

Use flexbox/grid that adapts to content

Test with longest language (usually German)

Avoid fixed widths on text containers

// ❌ Bad: Assumes short English text
<button className="w-24">Submit</button>

// ✅ Good: Adapts to content
<button className="px-4 py-2">Submit</button>

RTL (Right-to-Left) support:

/* Use logical properties */
margin-inline-start: 1rem; /* Not margin-left */
padding-inline: 1rem; /* Not padding-left/right */
border-inline-end: 1px solid; /* Not border-right */

/* Or use dir attribute */
[dir="rtl"] .arrow { transform: scaleX(-1); }

Character set support:

Use UTF-8 encoding everywhere

Test with Chinese/Japanese/Korean (CJK) characters

Test with emoji (they can be 2-4 bytes)

Handle different scripts (Latin, Cyrillic, Arabic, etc.)

Date/Time formatting:

// ✅ Use Intl API for proper formatting
new Intl.DateTimeFormat('en-US').format(date); // 1/15/2024
new Intl.DateTimeFormat('de-DE').format(date); // 15.1.2024

new Intl.NumberFormat('en-US', { 
  style: 'currency', 
  currency: 'USD' 
}).format(1234.56); // $1,234.56

Pluralization:

// ❌ Bad: Assumes English pluralization
`${count} item${count !== 1 ? 's' : ''}`

// ✅ Good: Use proper i18n library
t('items', { count }) // Handles complex plural rules

Error Handling

Network errors:

Show clear error messages

Provide retry button

Explain what happened

Offer offline mode (if applicable)

Handle timeout scenarios

// Error states with recovery
{error && (
  <ErrorMessage>
    <p>Failed to load data. {error.message}</p>
    <button onClick={retry}>Try again</button>
  </ErrorMessage>
)}

Form validation errors:

Inline errors near fields

Clear, specific messages

Suggest corrections

Don't block submission unnecessarily

Preserve user input on error

API errors:

Handle each status code appropriately

400: Show validation errors

401: Redirect to login

403: Show permission error

404: Show not found state

429: Show rate limit message

500: Show generic error, offer support

Graceful degradation:

Core functionality works without JavaScript

Images have alt text

Progressive enhancement

Fallbacks for unsupported features

Edge Cases & Boundary Conditions

Empty states:

No items in list

No search results

No notifications

No data to display

Provide clear next action

Loading states:

Initial load

Pagination load

Refresh

Show what's loading ("Loading your projects...")

Time estimates for long operations

Large datasets:

Pagination or virtual scrolling

Search/filter capabilities

Performance optimization

Don't load all 10,000 items at once

Concurrent operations:

Prevent double-submission (disable button while loading)

Handle race conditions

Optimistic updates with rollback

Conflict resolution

Permission states:

No permission to view

No permission to edit

Read-only mode

Clear explanation of why

Browser compatibility:

Polyfills for modern features

Fallbacks for unsupported CSS

Feature detection (not browser detection)

Test in target browsers

Onboarding & First-Run Experience

Production-ready features work for first-time users, not just power users. Design the paths that get new users to value:

Empty states: Every zero-data screen needs:

What will appear here (description or illustration)

Why it matters to the user

Clear CTA to create the first item or start from a template

Visual interest (not just blank space with "No items yet")

Empty state types to handle:

First use: emphasize value, provide templates

User cleared: light touch, easy to recreate

No results: suggest a different query, offer to clear filters

No permissions: explain why, how to get access

First-run experience: Get users to their "aha moment" as quickly as possible.

Show, don't tell -- working examples over descriptions

Progressive disclosure -- teach one thing at a time, not everything upfront

Make onboarding optional -- let experienced users skip

Provide smart defaults so required setup is minimal

Feature discovery: Teach features when users need them, not upfront.

Contextual tooltips at point of use (brief, dismissable, one-time)

Badges or indicators on new or unused features

Celebrate activation events quietly (a toast, not a modal)

NEVER:

Force long onboarding before users can touch the product

Show the same tooltip repeatedly (track and respect dismissals)

Block the entire UI during a guided tour

Create separate tutorial modes disconnected from the real product

Design empty states that just say "No items" with no next action

Input Validation & Sanitization

Client-side validation:

Required fields

Format validation (email, phone, URL)

Length limits

Pattern matching

Custom validation rules

Server-side validation (always):

Never trust client-side only

Validate and sanitize all inputs

Protect against injection attacks

Rate limiting

Constraint handling:

<!-- Set clear constraints -->
<input 
  type="text"
  maxlength="100"
  pattern="[A-Za-z0-9]+"
  required
  aria-describedby="username-hint"
/>
<small id="username-hint">
  Letters and numbers only, up to 100 characters
</small>

Accessibility Resilience

Keyboard navigation:

All functionality accessible via keyboard

Logical tab order

Focus management in modals

Skip links for long content

Screen reader support:

Proper ARIA labels

Announce dynamic changes (live regions)

Descriptive alt text

Semantic HTML

Motion sensitivity:

@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

High contrast mode:

Test in Windows high contrast mode

Don't rely only on color

Provide alternative visual cues

Performance Resilience

Slow connections:

Progressive image loading

Skeleton screens

Optimistic UI updates

Offline support (service workers)

Memory leaks:

Clean up event listeners

Cancel subscriptions

Clear timers/intervals

Abort pending requests on unmount

Throttling & Debouncing:

// Debounce search input
const debouncedSearch = debounce(handleSearch, 300);

// Throttle scroll handler
const throttledScroll = throttle(handleScroll, 100);

Testing Strategies

Manual testing:

Test with extreme data (very long, very short, empty)

Test in different languages

Test offline

Test slow connection (throttle to 3G)

Test with screen reader

Test keyboard-only navigation

Test on old browsers

Automated testing:

Unit tests for edge cases

Integration tests for error scenarios

E2E tests for critical paths

Visual regression tests

Accessibility tests (axe, WAVE)

IMPORTANT: Hardening is about expecting the unexpected. Real users will do things you never imagined.

NEVER:

Assume perfect input (validate everything)

Ignore internationalization (design for global)

Leave error messages generic ("Error occurred")

Forget offline scenarios

Trust client-side validation alone

Use fixed widths for text

Assume English-length text

Block entire interface when one component errors

Verify Hardening

Test thoroughly with edge cases:

Long text: Try names with 100+ characters

Emoji: Use emoji in all text fields

RTL: Test with Arabic or Hebrew

CJK: Test with Chinese/Japanese/Korean

Network issues: Disable internet, throttle connection

Large datasets: Test with 1000+ items

Concurrent actions: Click submit 10 times rapidly

Errors: Force API errors, test all error states

Empty: Remove all data, test empty states

Remember: You're hardening for production reality, not demo perfection. Expect users to input weird data, lose connection mid-flow, and use your product in unexpected ways. Build resilience into every component.