Auto-Generate DTOs from JSON API Responses

Working with third-party APIs means writing a lot of DTOs. So I built a quick code generator that turns JSON fixtures into typed PHP classes.

The workflow:

1. Capture fixtures: add HTTP middleware to dump API responses to JSON files
2. Analyze schema: scan fixtures, merge similar structures, infer types
3. Generate DTOs: output properly typed classes with serializer annotations

php artisan generate:dtos \
  --output=app/Services/SDK/ThirdParty \
  --namespace="App\\Services\\SDK\\ThirdParty"

The generator handles:

• Type inference from JSON values (string/int/float/bool/null)
• Nullability detection: if a field is missing in any fixture, it’s nullable
• Nested objects: creates separate classes for complex types
• Array types: uses Str::singular() to name item classes (products → Product)

This saved hours of manual DTO writing. The key insight: API responses are the source of truth. Let the actual data structure define your types, not the other way around.