This error occurs when angular cannot find `.angular-cli.json` file (Do note there is a dot in the file name). Usually it is a hidden file.
Try these steps first: --- - Delete your `node_modules` folder and `package-lock.json` file - npm install - npm uninstall -g angular-cli - npm uninstall -g @angular/cli - npm install -g @angular/cli - ng serve
If it still produces the same error, then you will actually need `.angular-cli.json` file.
**Default `.angular-cli.json` file:** { "$schema": "./node_modules/@angular/cli/lib/config/schema.json", "project": { "name": "PROJECT_NAME" }, "apps": [ { "root": "src", "outDir": "dist", "assets": [ "assets", "favicon.ico" ], "index": "index.html", "main": "main.ts", "polyfills": "polyfills.ts", "test": "test.ts", "tsconfig": "tsconfig.app.json", "testTsconfig": "tsconfig.spec.json", "prefix": "app", "styles": [ "styles.css" ], "scripts": [], "environmentSource": "environments/environment.ts", "environments": { "dev": "environments/environment.ts", "prod": "environments/environment.prod.ts" } } ], "e2e": { "protractor": { "config": "./protractor.conf.js" } }, "lint": [ { "project": "src/tsconfig.app.json" }, { "project": "src/tsconfig.spec.json" }, { "project": "e2e/tsconfig.e2e.json" } ], "test": { "karma": { "config": "./karma.conf.js" } }, "defaults": { "styleExt": "css", "component": {} } }
**Note:** This is just a default file, you will need to configure your project settings in this file.

**This is a working solution until Angular v5 because inside v6, the location of the file changed to angular.json, and changed also the content**
Create a new file called *.angular-cli.json* and insert:
{ "$schema": "./node_modules/@angular/cli/lib/config/schema.json", "project": { "name": "PROJECT_NAME" }, "apps": [ { "root": "src", "outDir": "dist", "assets": [ "assets", "favicon.ico" ], "index": "index.html", "main": "main.ts", "polyfills": "polyfills.ts", "test": "test.ts", "tsconfig": "tsconfig.app.json", "testTsconfig": "tsconfig.spec.json", "prefix": "app", "styles": [ "styles.css" ], "scripts": [], "environmentSource": "environments/environment.ts", "environments": { "dev": "environments/environment.ts", "prod": "environments/environment.prod.ts" } } ], "e2e": { "protractor": { "config": "./protractor.conf.js" } }, "lint": [ { "project": "src/tsconfig.app.json" }, { "project": "src/tsconfig.spec.json" }, { "project": "e2e/tsconfig.e2e.json" } ], "test": { "karma": { "config": "./karma.conf.js" } }, "defaults": { "styleExt": "css", "component": {} } }
You will also find a copy of this json if you create a new project from [angular-cli][1].

[1]: https://cli.angular.io/