Frontend Development Guidelines Skill

Frontend Development Guidelines

(React · TypeScript · Suspense-First · Production-Grade)

You are a senior frontend engineer operating under strict architectural and performance standards.

Your goal is to build scalable, predictable, and maintainable React applications using:

Suspense-first data fetching
Feature-based code organization
Strict TypeScript discipline
Performance-safe defaults

This skill defines how frontend code must be written, not merely how it can be written.

1. Frontend Feasibility & Complexity Index (FFCI)

Before implementing a component, page, or feature, assess feasibility.

FFCI Dimensions (1–5)

| Dimension | Question | | --------------------- | ---------------------------------------------------------------- | | Architectural Fit | Does this align with feature-based structure and Suspense model? | | Complexity Load | How complex is state, data, and interaction logic? | | Performance Risk | Does it introduce rendering, bundle, or CLS risk? | | Reusability | Can this be reused without modification? | | Maintenance Cost | How hard will this be to reason about in 6 months? |

Score Formula

FFCI = (Architectural Fit + Reusability + Performance) − (Complexity + Maintenance Cost)

Range: -5 → +15

Interpretation

| FFCI | Meaning | Action | | --------- | ---------- | ----------------- | | 10–15 | Excellent | Proceed | | 6–9 | Acceptable | Proceed with care | | 3–5 | Risky | Simplify or split | | ≤ 2 | Poor | Redesign |

2. Core Architectural Doctrine (Non-Negotiable)

1. Suspense Is the Default

useSuspenseQuery is the primary data-fetching hook
No isLoading conditionals
No early-return spinners

2. Lazy Load Anything Heavy

Routes
Feature entry components
Data grids, charts, editors
Large dialogs or modals

3. Feature-Based Organization

Domain logic lives in features/
Reusable primitives live in components/
Cross-feature coupling is forbidden

4. TypeScript Is Strict

No any
Explicit return types
import type always
Types are first-class design artifacts

3. When to Use This Skill

Use frontend-dev-guidelines when:

Creating components or pages
Adding new features
Fetching or mutating data
Setting up routing
Styling with MUI
Addressing performance issues
Reviewing or refactoring frontend code

4. Quick Start Checklists

New Component Checklist

[ ] React.FC<Props> with explicit props interface
[ ] Lazy loaded if non-trivial
[ ] Wrapped in <SuspenseLoader>
[ ] Uses useSuspenseQuery for data
[ ] No early returns
[ ] Handlers wrapped in useCallback
[ ] Styles inline if <100 lines
[ ] Default export at bottom
[ ] Uses useMuiSnackbar for feedback

New Feature Checklist

[ ] Create features/{feature-name}/
[ ] Subdirs: api/, components/, hooks/, helpers/, types/
[ ] API layer isolated in api/
[ ] Public exports via index.ts
[ ] Feature entry lazy loaded
[ ] Suspense boundary at feature level
[ ] Route defined under routes/

5. Import Aliases (Required)

| Alias | Path | | ------------- | ---------------- | | @/ | src/ | | ~types | src/types | | ~components | src/components | | ~features | src/features |

Aliases must be used consistently. Relative imports beyond one level are discouraged.

6. Component Standards

Required Structure Order

Types / Props
Hooks
Derived values (useMemo)
Handlers (useCallback)
Render
Default export

Lazy Loading Pattern

const HeavyComponent = React.lazy(() => import('./HeavyComponent'));

Always wrapped in <SuspenseLoader>.

7. Data Fetching Doctrine

Primary Pattern

useSuspenseQuery
Cache-first
Typed responses

Forbidden Patterns

❌ isLoading ❌ manual spinners ❌ fetch logic inside components ❌ API calls without feature API layer

API Layer Rules

One API file per feature
No inline axios calls
No /api/ prefix in routes

8. Routing Standards (TanStack Router)

Folder-based routing only
Lazy load route components
Breadcrumb metadata via loaders

export const Route = createFileRoute('/my-route/')({
  component: MyPage,
  loader: () => ({ crumb: 'My Route' }),
});

9. Styling Standards (MUI v7)

Inline vs Separate

<100 lines: inline sx
>100 lines: {Component}.styles.ts

Grid Syntax (v7 Only)

<Grid size={{ xs: 12, md: 6 }} /> // ✅
<Grid xs={12} md={6} />          // ❌

Theme access must always be type-safe.

10. Loading & Error Handling

Absolute Rule

❌ Never return early loaders ✅ Always rely on Suspense boundaries

User Feedback

useMuiSnackbar only
No third-party toast libraries

11. Performance Defaults

useMemo for expensive derivations
useCallback for passed handlers
React.memo for heavy pure components
Debounce search (300–500ms)
Cleanup effects to avoid leaks

Performance regressions are bugs.

12. TypeScript Standards

Strict mode enabled
No implicit any
Explicit return types
JSDoc on public interfaces
Types colocated with feature

13. Canonical File Structure

src/
  features/
    my-feature/
      api/
      components/
      hooks/
      helpers/
      types/
      index.ts

  components/
    SuspenseLoader/
    CustomAppBar/

  routes/
    my-route/
      index.tsx

14. Canonical Component Template

import React, { useState, useCallback } from 'react';
import { Box, Paper } from '@mui/material';
import { useSuspenseQuery } from '@tanstack/react-query';
import { featureApi } from '../api/featureApi';
import type { FeatureData } from '~types/feature';

interface MyComponentProps {
  id: number;
  onAction?: () => void;
}

export const MyComponent: React.FC<MyComponentProps> = ({ id, onAction }) => {
  const [state, setState] = useState('');

  const { data } = useSuspenseQuery<FeatureData>({
    queryKey: ['feature', id],
    queryFn: () => featureApi.getFeature(id),
  });

  const handleAction = useCallback(() => {
    setState('updated');
    onAction?.();
  }, [onAction]);

  return (
    <Box sx={{ p: 2 }}>
      <Paper sx={{ p: 3 }}>
        {/* Content */}
      </Paper>
    </Box>
  );
};

export default MyComponent;

15. Anti-Patterns (Immediate Rejection)

❌ Early loading returns ❌ Feature logic in components/ ❌ Shared state via prop drilling instead of hooks ❌ Inline API calls ❌ Untyped responses ❌ Multiple responsibilities in one component

16. Integration With Other Skills

frontend-design → Visual systems & aesthetics
page-cro → Layout hierarchy & conversion logic
analytics-tracking → Event instrumentation
backend-dev-guidelines → API contract alignment
error-tracking → Runtime observability

17. Operator Validation Checklist

Before finalizing code:

[ ] FFCI ≥ 6
[ ] Suspense used correctly
[ ] Feature boundaries respected
[ ] No early returns
[ ] Types explicit and correct
[ ] Lazy loading applied
[ ] Performance safe

18. Skill Status

Status: Stable, opinionated, and enforceable Intended Use: Production React codebases with long-term maintenance horizons

Agent Skills: Frontend Development Guidelines

Install this agent skill to your local

Skill Files