TypeScript strictness configuration

A type checker that admits any and unchecked access is a linter, not a safety net. Configure tsconfig.json so the compiler catches the errors it is capable of catching, and adopt the stricter flags deliberately rather than all at once.

Baseline (table stakes)

• New TypeScript projects MUST set "strict": true in tsconfig.json compilerOptions. This enables the strict family as a unit (strictNullChecks, noImplicitAny, strictFunctionTypes, strictBindCallApply, useUnknownInCatchVariables, and others).
• Code MUST NOT silence the checker with project-wide // @ts-nocheck, blanket any, or skipLibCheck used to hide first-party errors. Use a narrowly-scoped // @ts-expect-error (with a reason) for the rare unavoidable case so the suppression fails loudly if the underlying type later changes.
• Disabling individual strict-family flags (e.g. "strictNullChecks": false) SHOULD be treated as a temporary migration state, recorded in code with a tracking reference — not a permanent posture.

Recommended near-defaults

Enable these on greenfield projects; they close gaps strict alone leaves open.

• New projects SHOULD enable noUncheckedIndexedAccess and verbatimModuleSyntax.
• With verbatimModuleSyntax, type-only imports MUST use import type / export type (or inline type modifiers), since the compiler no longer elides them automatically.

Optional, situational flags

• exactOptionalPropertyTypes (TS 4.4) — distinguishes a missing property from one explicitly set to undefined. Enable when modeling APIs where "absent" and "present but undefined" differ. It adds real friction with loosely-typed third-party shapes, so it is opt-in, not a baseline.
• erasableSyntaxOnly (TS 5.8) — errors on TypeScript constructs that emit runtime code (enum, namespace with runtime members, parameter properties). Enable it when files are run via native type-stripping (Node.js --experimental-strip-types/stable type stripping, Bun, Deno, or in-browser transforms) so the source contains no non-erasable syntax. Pair it with verbatimModuleSyntax.

Adopt incrementally on existing code

The stricter flags surface real defects but generate large error volumes on legacy code. Per agenticdevelopercookbook://principles/small-reversible-decisions:

• Turn on strict first; land that as its own change.
• Enable one stricter flag at a time (noUncheckedIndexedAccess, then exactOptionalPropertyTypes, etc.), fixing the fallout before moving on.
• Agents SHOULD NOT enable every flag in a single sweep on an established codebase — small, reviewable diffs keep each step reversible.

FORECAST — not yet relied upon as shipped

Treat the following as roadmap/proposed behavior. Do not write configs or guidance that assume it as current.

• The native Go compiler ("tsgo", "Project Corsa") and the TypeScript 7.0 line are a proposed reimplementation targeting large build speedups. As of this writing, confirm actual release state against the official TypeScript blog and microsoft/typescript-go before depending on it.
• "strict by default" and the removal of legacy module/target modes (e.g. dropping node10 resolution, raising the minimum target) are PLANNED breaking changes discussed for the 6.0/7.0 line. Until you have verified them in shipped release notes, MUST keep setting "strict": true explicitly rather than relying on an implicit default.

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