Request Validation

This Skill provides Claude Code with specific guidance on how it should handle global validation.

When to use this skill:

• Validating API request bodies in Express handlers
• Creating TypeScript type guard functions
• Checking RenderRequest fields (month, year, books)
• Validating RecapBook data structure and completeness
• Implementing field-specific validation logic
• Returning structured validation error responses

Instructions

• TypeScript Type Guards: Use TypeScript types and type guards for compile-time and runtime validation
• Server-Side Validation: All API endpoints must validate request bodies against defined types
• Fail Early: Validate input at API boundary; reject invalid requests before processing
• Specific Error Messages: Return clear, field-specific errors: { error: 'Invalid month', field: 'month' }
• Request Body Validation: Validate RenderRequest fields (month 1-12, year valid, books array structure)
• Type Safety: Define interfaces in src/lib/types.ts and enforce at API boundaries
• Business Rule Validation: Validate video constraints (frame counts, durations, book data completeness)
• No Client-Side Validation: This is a server-to-server API; all validation happens server-side

Examples:

// Good: Type guards, early validation, specific errors
import { RenderRequest, RecapBook } from '@/lib/types';

function isValidRenderRequest(body: any): body is RenderRequest {
  return (
    typeof body.month === 'number' &&
    body.month >= 1 && body.month <= 12 &&
    typeof body.year === 'number' &&
    body.year >= 2000 && body.year <= 2100 &&
    Array.isArray(body.books)
  );
}

app.post('/render', async (req, res) => {
  if (!isValidRenderRequest(req.body)) {
    return res.status(400).json({
      error: 'Invalid request',
      details: 'month (1-12) and year (2000-2100) required'
    });
  }

  const request: RenderRequest = req.body;
  // Now TypeScript knows the shape is correct
});

// Bad: No validation, assumes input is correct
app.post('/render', async (req, res) => {
  const { month, year } = req.body;
  const result = await renderVideo(month, year);
  res.json(result);
});