# TypeScript Production Readiness Checklist: What to Verify Before You Ship > A practical checklist covering TypeScript configuration, runtime safety, CI integration, and type discipline before deploying a production TypeScript app. - **Published:** 2026-01-14 - **Author:** Clixo - **Reading time:** 5 min read - **Tags:** typescript, checklist, production, deployment, type-safety - **Canonical URL:** https://clixo.sh/blog/typescript-production-checklist-before-shipping Shipping a TypeScript app is not the same as shipping a type-safe app. The language gives you tools. Whether your codebase uses them well is a separate question. Before your next production deployment, run through this checklist to verify your TypeScript setup is actually protecting you. ## TypeScript Production Readiness Checklist ### Configuration - **`strict: true` is set in tsconfig.json.** This enables the eight flags — `strictNullChecks`, `noImplicitAny`, `strictFunctionTypes`, and five others — that provide real type safety. If you inherited a codebase with strict off, plan a migration path. Ship with strict on or accept that TypeScript is providing limited value. - **`noUncheckedIndexedAccess: true` is set.** This flag is not included in `strict: true`. Without it, array index access and object key access return `T` even when the value can be `undefined`. Enable it and fix the errors — they are real bugs. - **`noImplicitReturns: true` is set.** Ensures every code path through a function with a return type actually returns. Catches the silent `undefined` that slips out when a branch is forgotten. - **`skipLibCheck` is `false` unless justified.** If it is `true`, document why. Skipping type checking on declaration files hides real problems in third-party types. - **`target` matches your actual runtime.** If you are running Node 22, your target should be `ES2022` or higher. Compiling to `ES5` adds unnecessary code and polyfills. - **`moduleResolution` is `NodeNext` or `Bundler` — not `node`.** The legacy `node` resolution does not handle modern ESM correctly. Update it. ### Runtime Validation - **External data is validated at every ingestion point.** JSON from HTTP APIs, data from database queries, webhook payloads, and message queue events are all untyped at runtime. If your application calls `data as SomeType` anywhere without prior validation, that is an unguarded trust boundary. Every one should use a schema library (Zod, Valibot, Arktype) or explicit checks. - **Environment variables are validated at startup.** `process.env.SOME_KEY` is `string | undefined`. If your application assumes it is always defined, a deployment missing a variable will fail at the point of use — not at startup. Validate all required environment variables when the process boots and throw immediately if any are missing. - **Error handling does not blindly cast `err` to `Error`.** Thrown values can be anything. Use `err instanceof Error` before accessing `.message`. With `useUnknownInCatchVariables` on, TypeScript will remind you if you forget. ### Type Discipline - **No `any` types are used without explicit justification.** Search the codebase for `any`. Some uses are unavoidable (complex third-party interop), but most are avoidable. Each one is a hole in your type coverage. Consider `unknown` instead — it forces you to narrow before use. - **Type assertions (`as SomeType`) are rare and reviewed.** Every `as` is a promise you are making to TypeScript. If you are wrong, you get a runtime crash. Find all occurrences and verify each one is genuinely safe or has runtime validation backing it. - **Non-null assertions (`!`) are rare.** Same reasoning as `as`. Each `!` is a suppressed null check. If the value is ever actually null, you get a crash. Replace with explicit guards where possible. - **Shared interfaces and types live in a `types/` directory.** Centralized type definitions prevent duplication and drift. If the same interface is defined in two places, they will diverge. - **Return types are explicit on public functions.** TypeScript infers return types, but annotating them explicitly catches implementation drift. If a function is supposed to return `Promise` and you change the implementation, an explicit return type annotation will surface the error immediately. ### CI and Build Pipeline ```mermaid flowchart LR SRC["Source Code"] --> TC["tsc --noEmit"] SRC --> TESTS["Type-Checked Tests"] TC -->|"fails"| BLOCK["Block Merge"] TESTS -->|"fails"| BLOCK TC -->|"passes"| BUILD["Production Build"] TESTS -->|"passes"| BUILD BUILD --> DEPLOY["Deploy"] ``` - **`tsc --noEmit` runs on every pull request.** Type checking should be a separate step from building. Run it in CI and block merges on failure. - **Type check is not skipped to speed up CI.** Skipping type checks to save build minutes defeats the purpose of using TypeScript. If type checking is slow, investigate project references and incremental builds — not disabling it. - **The build output is from the same tsconfig that type-checks.** If your CI type-checks with one config and builds with another (common in monorepos), divergence is possible. Align them. - **Tests are type-checked too.** If your test files use `ts-jest` or Vitest with TypeScript, ensure they are included in the tsconfig. Typed tests surface usage errors and keep test code honest. ### Dependencies - **`@types/*` packages match the version of the underlying library.** A mismatch between `express` and `@types/express` versions can cause subtle type errors or incorrect inference. Pin them together. - **Dependencies without type definitions are wrapped.** If a package ships no `.d.ts` files and no community types exist, write a minimal declaration file in `src/@types/`. Do not let the entire import become `any`. --- If any item on this list is an open question for your team, that is where to invest before the next deployment. 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