angular/angular-cli · error · Error

The '@angular-devkit/build-angular/plugins/karma' karma plug

Error message

The '@angular-devkit/build-angular/plugins/karma' karma plugin is meant to be used from within Angular CLI and will not work correctly outside of it.

What it means

The karma plugin shipped at @angular-devkit/build-angular/plugins/karma requires `config.buildWebpack` (options + logger) which only the Angular CLI's karma builder injects. When the plugin is loaded in a plain karma.conf.js run directly by karma (not via `ng test`), that field is absent and this error is thrown. It is an intentional guard: the plugin depends on CLI-provided webpack context.

Source

Thrown at packages/angular_devkit/build_angular/src/tools/webpack/plugins/karma/karma.ts:25

 */

/* eslint-disable */
// TODO: cleanup this file, it's copied as is from Angular CLI.
import type { IncomingMessage, ServerResponse } from 'node:http';
import * as path from 'node:path';
import type { Compiler } from 'webpack';
import webpackDevMiddleware from 'webpack-dev-middleware';

import { statsErrorsToString } from '../../utils/stats';
import { logging } from '@angular-devkit/core';
import { BuildOptions } from '../../../../utils/build-options';
import { normalizeSourceMaps } from '../../../../utils/index';

let webpackMiddleware: webpackDevMiddleware.API<IncomingMessage, ServerResponse>;

const init: any = (config: any, emitter: any) => {
  if (!config.buildWebpack) {
    throw new Error(
      `The '@angular-devkit/build-angular/plugins/karma' karma plugin is meant to` +
        ` be used from within Angular CLI and will not work correctly outside of it.`,
    );
  }
  const options = config.buildWebpack.options as BuildOptions;
  const logger: logging.Logger = config.buildWebpack.logger;

  // Add a reporter that fixes sourcemap urls.
  if (normalizeSourceMaps(options.sourceMap).scripts) {
    config.reporters.unshift('@angular-devkit/build-angular--sourcemap-reporter');

    // Code taken from https://github.com/tschaub/karma-source-map-support.
    // We can't use it directly because we need to add it conditionally in this file, and karma
    // frameworks cannot be added dynamically.
    const smsPath = path.dirname(require.resolve('source-map-support'));
    const ksmsPath = path.dirname(require.resolve('karma-source-map-support'));

    config.files.unshift(

View on GitHub (pinned to bb72145f9a)

Solutions

1. Run tests with `ng test` so the Angular CLI karma builder injects config.buildWebpack
2. Remove the '@angular-devkit/build-angular/plugins/karma' require from karma.conf.js if you are not using the CLI builder
3. If an IDE must launch tests, configure it to execute the `ng test` command (or the builder) rather than karma directly

Example fix

// before
karma start karma.conf.js
// after
ng test

// karma.conf.js
if (!config.buildWebpack) {
  throw new Error('Run via `ng test`; the build-angular karma plugin requires the CLI builder.');
}

function isCliDriven(config: any): config is { buildWebpack: { options: unknown; logger: unknown } } {
  return !!config && typeof config === 'object' && !!config.buildWebpack;
}

try {
  init(config, emitter);
} catch (err) {
  if (String(err.message).includes('meant to be used from within Angular CLI')) {
    console.error('Use `ng test` instead of invoking karma directly.');
    process.exit(1);
  }
  throw err;
}

When it happens

Trigger: Running `karma start karma.conf.js` directly (or via a test runner script) on a config that includes require('@angular-devkit/build-angular/plugins/karma'), so config.buildWebpack is never populated.

Common situations: IDE test runners (WebStorm/VS Code) launching karma directly instead of through `ng test`; CI scripts invoking karma CLI; migrating karma configs across projects where the CLI builder wiring was dropped.

Related errors

• Could not find ${level} workspace.
• Invalid config found at ${workspace.filePath}. CLI should be
• Could not find a ${level} workspace. Are you in a project?
• Could not find the '${builderConf}' builder's node package.
• Cannot determine project for command. This is a multi-projec

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/474490fde6fb4068. Report an issue: GitHub.