Which flags does --strict turn on?

The strict family enables noImplicitAny, strictNullChecks, strictFunctionTypes, strictBindCallApply, strictPropertyInitialization, noImplicitThis, useUnknownInCatchVariables and alwaysStrict. You can set --strict and then disable individual members if needed.

Do CLI flags and tsconfig keys differ?

They map one-to-one but differ in form. The CLI uses kebab-case with a leading double dash like --noImplicitAny, while tsconfig.json uses camelCase boolean or string values inside compilerOptions.

What does esModuleInterop do?

It generates helper code so default imports work against CommonJS modules that lack a default export, letting you write import express from "express". It implies allowSyntheticDefaultImports for type checking.

What is the difference between target and module?

target sets the JavaScript language level of emitted code, such as ES2022 down-levelling. module controls the module system of the output, such as ESNext, CommonJS or NodeNext, independent of the syntax level.

Does tsc need a tsconfig.json?

No. You can pass files and flags entirely on the command line, but a tsconfig.json is the standard way to configure a project so the same options apply consistently to every build and editor.

TypeScript Compiler Flags Reference

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Look up TypeScript compiler flags without the handbook

The TypeScript compiler tsc exposes dozens of flags that change type checking, the emitted JavaScript and module resolution. This reference lets you search every common flag by name or effect, filter by group, and see both the CLI form and the tsconfig.json compilerOptions equivalent along with its default. It runs entirely in your browser.

How it works

Each entry pairs the CLI flag (kebab-case, double-dash) with its tsconfig.json key (camelCase), records the default value, marks whether it is a member of the strict family, and explains its effect. The compiler reads compilerOptions from tsconfig.json, then applies any CLI overrides on top. Setting strict is shorthand that flips the whole strict family to true:

{
  "compilerOptions": {
    "strict": true,
    "target": "ES2022",
    "module": "NodeNext",
    "esModuleInterop": true,
    "skipLibCheck": true
  }
}

Tips and examples

Enable strict first, then relax individual members like noImplicitAny: false only where a gradual migration needs it.
noEmit: true makes tsc a pure type checker, useful in CI when a bundler like esbuild or SWC produces the actual JavaScript.
skipLibCheck: true skips type-checking .d.ts files and dramatically speeds up builds in large projects with many dependencies.
Use module: "NodeNext" with moduleResolution: "NodeNext" for modern Node ESM/CJS interop driven by each package’s type field and exports map.