| name | typescript-strict-migration |
| description | Migrate a TypeScript codebase toward compiler strict mode: inventory current flags, enable checks incrementally (strictNullChecks, noImplicitAny, and the rest of strict), use per-package or path-scoped tsconfigs, ts-migrate/codemod patterns, and temporary suppressions with a burn-down plan. Use when turning on strict, fixing mass tsc errors after strictNullChecks/noImplicitAny, or planning an incremental TS strict rollout without a big-bang rewrite.
|
TypeScript Strict Migration
Move a TS/TSX codebase to compiler strictness safely: measure error volume,
enable flags in a controlled order, fix or quarantine debt, and keep CI green.
This skill owns migration mechanics and flag sequencing. Day-to-day typing
hygiene and ESLint rules stay with typescript-style-and-eslint; reliability,
tests, and security stay with code-quality-standards.
When To Use
- Enabling
strict, strictNullChecks, noImplicitAny, or sibling flags on an existing app/lib
tsc error floods after a strict flip; need incremental path or package-by-package rollout- Adopting
ts-migrate, codemods, or path-scoped tsconfigs / project references for strict
- Burning down
// @ts-nocheck, blanket any, or unchecked JS allowlists
- Mentions: TypeScript strict mode, strictNullChecks migration, noImplicitAny backlog, ts-migrate, incremental strict enablement
Do not use as primary for:
| Need | Skill instead |
|---|
Everyday TS style, ESLint no-explicit-any, import order | typescript-style-and-eslint |
| Prettier vs ESLint format ownership | prettier-eslint-editorconfig |
| Behavior, errors, tests, security of fixed code | code-quality-standards |
| New greenfield TS with strict already on | typescript-style-and-eslint + CQS |
Repo Config First
Repo compiler and CI settings outrank defaults below.
- tsconfig graph: root
tsconfig.json, tsconfig.app/build/test.json, project references, extends chains
- Current flags:
strict and each sub-flag; allowJs, checkJs, skipLibCheck, noEmit / build mode
- CI typecheck: which config CI runs (
tsc -b, tsc --noEmit, Nx/Turbo target) — migrate that path first
- Monorepo boundaries: packages that can go strict independently; shared types packages first when feasible
- Existing suppressions:
@ts-nocheck, @ts-ignore / @ts-expect-error, any density, // @ts-check JS
- Tooling: ESLint
@typescript-eslint, ts-migrate, typescript-eslint type-aware rules already on
- Neighbor patterns: prior migrations, path-mapped strict overlays, exclude globs
Precedence: Follow the repo’s package manager, composite projects, and CI. Propose flag flips only with a measured error budget and exit criteria.
Workflow
-
Baseline. Run the repo typecheck command; capture error count by code (TS7006, TS2322, TS2345, TS2531/TS2532, TS18048, etc.) and by directory/package. Record current strict* flags. Do not flip everything in one PR on a large dirty tree without a quarantine plan.
-
Choose a rollout shape.
| Shape | When | Notes |
|---|
| Package-by-package | Monorepo / clear package boundaries | Strict in leaf libs first, then apps |
| Path-scoped overlay | One app, hot dirs first | Extra tsconfig.strict.json include/files or project ref |
| Flag-by-flag | Single package, moderate errors | Enable one sub-flag per milestone |
| Codemod + fix | Huge implicit-any / null noise | ts-migrate / scripted inserts, then human fix |
| Big-bang | Small repo or already near-clean | Only if baseline is low and CI can absorb |
-
Prefer explicit sub-flags before or with strict. strict: true turns on the family together. On dirty codebases, enable high-value flags in order (adjust to measured top codes):
noImplicitAny — forces parameter/return annotation debt into the openstrictNullChecks — usually the largest semantic win and the largest diffstrictFunctionTypes, strictBindCallApply, strictPropertyInitializationnoImplicitThis, useUnknownInCatchVariables, alwaysStrict- Related non-
strict companions when ready: noUncheckedIndexedAccess, exactOptionalPropertyTypes, noImplicitReturns, noFallthroughCasesInSwitch, noPropertyAccessFromIndexSignature
-
Temporary tactics (always with burn-down):
Routing
| Situation | Primary | Helper |
|---|
| Strict rollout, flag order, ts-migrate, error burn-down | This skill | — |
| Style, ESLint typing rules, import order after types settle | typescript-style-and-eslint | this during migration |
| Format pipeline only | prettier-eslint-editorconfig | — |
| Implementation quality of runtime fixes/tests | code-quality-standards | always on code changes |
| JSDoc/TSDoc for public APIs touched in migration | docstring-and-typedoc | this for compiler flags |
typescript-style-and-eslint: hand off once flags are decided and bulk errors are under control; that skill owns ongoing any bans, assertion hygiene, and ESLint interplay. Keep this skill primary while sequencing flags and quarantine.code-quality-standards: apply whenever migration edits runtime behavior (null guards, API normalization, init order): explicit errors, tests for boundary null/undefined, no secrets in logs, no silent catch.
Output Checklist
