Why TypeScript is Essential for AI SaaS
LLMs return unstructured data. Users send unexpected inputs. External APIs break. TypeScript with strict mode and Zod catches entire categories of runtime bugs before they reach production — critical when every unhandled error costs you a customer.
1. Enable Strict Mode
In tsconfig.json: "strict": true, "noUncheckedIndexedAccess": true, "noImplicitReturns": true. This is non-negotiable for production AI apps.
2. Type LLM Responses with Zod + generateObject
Use the Vercel AI SDK's generateObject with a Zod schema to get fully typed, validated AI outputs. Never trust raw LLM JSON — always validate through a schema.
3. Discriminated Unions for AI States
Model your AI request lifecycle as a discriminated union: idle | loading | success | error. TypeScript forces you to handle every case in your UI, preventing the "blank screen" bug when AI calls fail.
4. Type-Safe Environment Variables
Parse process.env through a Zod schema at startup. Your app fails fast with a clear error if a required env var is missing — instead of a cryptic 500 error in production.
5. Avoid Common Anti-Patterns
Never use as any. Never use type assertions without runtime validation. Avoid @ts-ignore — use @ts-expect-error with a comment. Don't use object or {} as types.