Building a Type-Safe REST API with Zod, Express, and TypeScript: From Validation to OpenAPI Docs

Every REST API needs input validation and documentation. Most teams treat these as separate concerns — writing Joi schemas for validation, then manually maintaining OpenAPI specs. They inevitably drift apart. Here'''s how to use Zod as the single source of truth for both. What We'''re Building A complete REST API for a task management system with: Request/response validation using Zod schemas Automatic OpenAPI 3.1 spec generation from those schemas Type-safe request handlers (no any types) Proper error responses with structured validation messages Prerequisites Node.js 20+ and npm Basic TypeScript and Express knowledge Familiarity with REST API concepts Project Setup mkdir task-api && cd task-api npm init -y npm install express zod zod-to-openapi uuid npm install -D typescript @types/express @types/uuid tsx Create tsconfig.json : { "compilerOptions" : { "target" : "ES2022" , "module" : "NodeNext" , "moduleResolution" : "NodeNext" , "strict" : true , "esModuleInterop" : true , "outDir"