TypeScript error TS2307: 'Cannot find module X or its corresponding type declarations' (or TS7016: 'Could not find a declaration file for module X'). How do I fix it?

Cause: TypeScript can't resolve the import to a file with types. Common reasons: the package isn't installed in this project (or the editor is using a different folder's node_modules); the package ships no types and its @types/X package isn't installed (that gives TS7016); a path alias like @/components isn't configured in tsconfig paths (or your bundler config doesn't match); module/moduleResolution settings don't match how the package publishes its files (for example a package that only declares types through package.json 'exports' needs moduleResolution 'node16', 'nodenext' or 'bundler'); or the import is for a non-code file (.css, .svg, .png) with no declaration. Fix (by cause): 1. Missing package: npm install X (check it's in this project's package.json), then restart the TypeScript server in your editor. 2. No bundled types: npm install -D @types/X. If none exist, add a small declaration file (for example src/types/x.d.ts with declare module 'X';) and make sure it's included by tsconfig 'include'. 3. Path aliases: set compilerOptions.baseUrl/paths in tsconfig.json to match your bundler's aliases (Vite resolve.alias, webpack resolve.alias, or use a plugin that reads tsconfig paths). Aliases in tsconfig alone don't change runtime resolution. 4. Resolution mode: for modern packages use moduleResolution 'bundler' (apps built by Vite/webpack/esbuild) or 'nodenext' with module 'nodenext' (code run directly by Node); the old 'node'/'node10' mode ignores package 'exports'. 5. Asset imports: add declarations such as declare module '*.svg'; (many frameworks provide these via a types reference like vite/client). 6. Monorepos: make sure the dependency is built (its .d.ts files exist) or use project references, and that the editor opened the right workspace. Verify: npx tsc --noEmit passes, and npx tsc --traceResolution | grep X shows where TypeScript found the module. Sources: https://www.typescriptlang.org/docs/handbook/modules/reference.html https://www.typescriptlang.org/tsconfig/ https://www.typescriptlang.org/docs/handbook/declaration-files/consumption.html