angular/angular-cli · error · Error

Webpack Dev Server configuration was not set.

Error message

Webpack Dev Server configuration was not set.

What it means

After generating the webpack configuration via generateWebpackConfig (combining dev-server, common, and styles configs), setup() asserts that a devServer section exists. A missing devServer config means the generated config is structurally wrong (e.g. wrong mode/optimization resolution), so the server cannot be started and the builder throws.

Source

Thrown at packages/angular_devkit/build_angular/src/builders/dev-server/webpack-server.ts:131

      logger.error(tags.stripIndents`
        ****************************************************************************************
        This is a simple server for use in testing or debugging Angular applications locally.
        It hasn't been reviewed for security issues.

        DON'T USE IT FOR PRODUCTION!
        ****************************************************************************************
      `);
    }

    const { config, i18n } = await generateI18nBrowserWebpackConfigFromContext(
      browserOptions,
      context,
      (wco) => [getDevServerConfig(wco), getCommonConfig(wco), getStylesConfig(wco)],
      options,
    );

    if (!config.devServer) {
      throw new Error('Webpack Dev Server configuration was not set.');
    }

    let locale: string | undefined;
    if (i18n.shouldInline) {
      // Dev-server only supports one locale
      locale = [...i18n.inlineLocales][0];
    } else if (i18n.hasDefinedSourceLocale) {
      // use source locale if not localizing
      locale = i18n.sourceLocale;
    }

    let webpackConfig = config;

    // If a locale is defined, setup localization
    if (locale) {
      if (i18n.inlineLocales.size > 1) {
        throw new Error(
          'The development server only supports localizing a single locale per build.',

View on GitHub (pinned to bb72145f9a)

Solutions

1. Restore clean dev-server options in angular.json (regenerate the target or compare against a fresh project) and re-run.
2. Reinstall/align @angular-devkit/build-angular and webpack-dev-server versions (delete node_modules and lockfile, reinstall).
3. If custom code overrides config generation, ensure it spreads/keeps config.devServer instead of replacing the config.
4. Run the stock 'ng serve' without custom builders/patches to isolate the source.

Example fix

// before (custom override)
webpackConfig = { ...webpackConfig, devServer: undefined };
// after
webpackConfig = { ...webpackConfig, devServer: { ...webpackConfig.devServer, port } };

function assertDevServerConfig(config: { devServer?: unknown }): asserts config is { devServer: object } {
  if (!config.devServer) {
    throw new Error('Generated webpack config has no devServer section; check angular.json dev-server options and versions.');
  }
}

const hasDevServer = (config: { devServer?: unknown }): config is { devServer: NonNullable<typeof config.devServer> } =>
  config.devServer != null;

try {
  await ngServe();
} catch (e) {
  if (String(e.message).includes('Webpack Dev Server configuration was not set')) {
    // reset angular.json dev-server target options / reinstall aligned versions
  }
  throw e;
}

When it happens

Trigger: generateWebpackConfig returns a config without a devServer property — typically due to corrupted or unsupported angular.json dev-server options (e.g. malformed 'buildTarget'/'browserTarget', invalid options merged through), a customization/patch of the dev-server config generation, or an incompatible @angular-devkit/build-angular / webpack-dev-server version combination.

Common situations: Hand-edited angular.json with invalid dev-server option types; monkey-patched generateWebpackConfig or custom builder extensions that drop devServer; version mismatch after upgrading webpack-dev-server (v3 vs v4 API changes) breaking config generation; calling setup() directly in custom builders with a mis-built config.

Related errors

• The "application" and "browser-esbuild" builders do not supp
• Only the "application" and "browser-esbuild" builders suppor
• Only the "application" and "browser-esbuild" builders suppor
• Webpack stats build result is required.
• Proxy configuration file ${proxyPath} does not exist.

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/528c3b9c96e89ead. Report an issue: GitHub.