typescript-strict

Replace any with unknown for untyped data, then narrow with type guards before use. For library boundaries that genuinely require any, add an eslint-disable comment explaining why. Use Record<string, unknown> for generic object shapes instead of any.

Use type guard functions with the is keyword, generics, or instanceof checks instead of as casts. For typed literals, use satisfies to validate shape while keeping narrow inference. Reserve as unknown as T for rare cases with a SAFETY comment.

Enable strict, noUnusedLocals, noUnusedParameters, noFallthroughCasesInSwitch, isolatedModules, and verbatimModuleSyntax as a baseline. For maximum strictness add exactOptionalPropertyTypes, noUncheckedSideEffectImports, erasableSyntaxOnly, and isolatedDeclarations.

Default to type for unions, intersections, mapped types, and props definitions. Use interface only when you need declaration merging or extends behavior, such as extending Record<string, unknown> for library-compatible node data.

Define a Zod schema for all environment variables and parse process.env at startup so the app fails fast on missing or invalid values. Keep secrets like database URLs unprefixed so they are never exposed to the browser bundle.

Only at third-party library integration boundaries where types genuinely require any, such as certain UI component props or extension APIs. Each occurrence must include an eslint-disable comment explaining the reason, and the project target is zero unexplained any usages.