TS7016: Could not find a declaration file for module

Most popular libraries have type definitions on DefinitelyTyped.

# Install type definitions
npm install --save-dev @types/lodash
npm install --save-dev @types/react
npm install --save-dev @types/express

# Check if types exist at:
# https://www.npmjs.com/search?q=%40types%2Fpackage-name

Create a .d.ts file to declare the module's types.

// custom.d.ts (in your project root or a types folder)
declare module "some-legacy-lib" {
  export function doSomething(input: string): void
  export const VERSION: string
  export default class LegacyAPI {
    constructor(options: Record<string, unknown>)
    run(): Promise<boolean>
  }
}

// Also include in tsconfig.json
// "include": ["src/**/*", "custom.d.ts"]

For quick fixes, declare the module as any to bypass type checking.

// global.d.ts
declare module "some-untyped-lib"  // Module typed as any

// This suppresses TS7016 but gives no type safety
import someLib from "some-untyped-lib"
// someLib is typed as any

Ensure TypeScript knows where to look for type declarations.

{
  "compilerOptions": {
    "typeRoots": [
      "./node_modules/@types",  // Default location
      "./src/types"              // Custom types folder
    ],
    "types": ["node", "express"],  // Auto-include specific @types
    "skipLibCheck": true            // Skip checking .d.ts files (faster)
  }
}