Full-Stack TypeScript: End-to-End Type Safety Architecture

Full-stack TypeScript uses the same language and shared type definitions across frontend, backend, and database layers. Type errors are caught at compile time, not runtime.

Shared types between layers: define types in a shared package (in a monorepo) or shared directory. API request/response types, database models, and business logic types are defined once and used everywhere.

tRPC: TypeScript-first API framework that provides end-to-end type safety without code generation. Define API procedures with input/output types, and the client automatically knows the API shape.

Zod for validation: define Zod schemas that serve as both runtime validation and TypeScript types. Use z.infer<typeof schema> to extract types from schemas. One definition, two purposes.

Prisma for database types: Prisma generates TypeScript types from your database schema. Schema changes automatically update types throughout your application. Database reality and code types stay synchronized.

API contract enforcement: whether using tRPC, REST with type generation, or GraphQL with codegen, ensure that API changes break the build if consumers are not updated. Compile-time API verification prevents runtime errors.

Form handling with type safety: React Hook Form + Zod resolver provides type-safe forms. Form data matches the Zod schema, which matches the API input type. Invalid data cannot reach the API.

Error handling types: define typed error responses for each API endpoint. Discriminated unions model different error types (ValidationError, NotFoundError, AuthError) with type-safe error handling.

Testing with types: TypeScript catches many bugs that tests would otherwise need to cover. Focus testing on business logic and integration points rather than type-level correctness.

Migration path: adopt full-stack TypeScript incrementally. Start with shared API types, add Zod validation, introduce Prisma for database types, and optionally adopt tRPC for new API endpoints.