{"record":{"id":"f43a4bd6c452ec4c","repo":"cypress-io/cypress","slug":"unsupported-webpackdevserver-version-webpackdevs","errorCode":null,"errorMessage":"Unsupported webpackDevServer version ${webpackDevServerMajorVersion}","messagePattern":"Unsupported webpackDevServer version (.+?)","errorType":"exception","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"npm/webpack-dev-server/src/createWebpackDevServer.ts","lineNumber":54,"sourceCode":"      webpack: {\n        module: webpack,\n      },\n      webpackDevServer: {\n        majorVersion: webpackDevServerMajorVersion,\n      },\n    },\n  } = config\n\n  const finalWebpackConfig = await makeWebpackConfig(config)\n  const webpackCompiler = webpack(finalWebpackConfig)\n\n  if (webpackDevServerMajorVersion === 5) {\n    debug('using webpack-dev-server v5')\n\n    return webpackDevServer5(config, webpackCompiler, finalWebpackConfig)\n  }\n\n  throw new Error(`Unsupported webpackDevServer version ${webpackDevServerMajorVersion}`)\n}\n\nfunction webpackDevServer5 (\n  config: CreateFinalWebpackConfig,\n  compiler: object,\n  finalWebpackConfig: Record<string, any>,\n) {\n  const { devServerConfig: { cypressConfig: { devServerPublicPathRoute } } } = config\n  const isOpenMode = !config.devServerConfig.cypressConfig.isTextTerminal\n  const WebpackDevServer = config.sourceWebpackModulesResult.webpackDevServer.module\n  const webpackDevServerConfig: WebpackDevServer5Configuration = {\n    host: '127.0.0.1',\n    port: 'auto',\n    // @ts-ignore\n    ...finalWebpackConfig?.devServer,\n    devMiddleware: {\n      publicPath: devServerPublicPathRoute,\n      stats: finalWebpackConfig.stats ?? 'minimal',","sourceCodeStart":36,"sourceCodeEnd":72,"githubUrl":"https://github.com/cypress-io/cypress/blob/0d85fdc91230885bca0a91df278312800a48b727/npm/webpack-dev-server/src/createWebpackDevServer.ts#L36-L72","documentation":"Thrown by createWebpackDevServer after constructing the webpack compiler: only webpack-dev-server major version 5 is handled; any other major version falls through to the throw. The major version is resolved from the user's installed webpack-dev-server module, so this fires when the installed major is not 5 (e.g. 4 or a future 6).","triggerScenarios":"Running CT with the webpack dev server when the resolved webpack-dev-server major version is not 5. The version is read from sourceWebpackModulesResult and compared at runtime; versions other than 5 have no handler branch.","commonSituations":"A project pinned to webpack-dev-server@4 (older), a future major (6+ not yet supported), or a transitive resolution that pulls a different major than expected. Also occurs after a fresh install where package.json does not pin webpack-dev-server@5.","solutions":["Install webpack-dev-server@5: `npm install -D webpack-dev-server@5 webpack@5`.","Ensure webpack and webpack-dev-server majors are compatible (both v5-line).","Remove conflicting resolutions/overrides that pull a different webpack-dev-server major.","If you must stay on v4, use an older @cypress/webpack-dev-server that supports it."],"exampleFix":"// before: package.json\n\"devDependencies\": { \"webpack-dev-server\": \"^4.15.1\" }\n// after\n\"devDependencies\": { \"webpack-dev-server\": \"^5.0.0\", \"webpack\": \"^5.0.0\" }","handlingStrategy":"validation","validationCode":"import { createRequire } from 'module'\nfunction ensureWebpackDevServerV5(root: string) {\n  const v = createRequire(import.meta.url)('webpack-dev-server/package.json', { paths: [root] }).version\n  if (!v.startsWith('5.')) throw new Error('Install webpack-dev-server@5')\n}","typeGuard":"const isWDSv5 = (v: string): boolean => v.startsWith('5.')","tryCatchPattern":null,"preventionTips":["Pin webpack-dev-server@^5 and webpack@^5 in devDependencies.","Add a preflight check that resolves the installed major before launching CT.","Avoid resolutions/overrides that change the webpack-dev-server major."],"tags":["webpack","dev-server","version-mismatch","dependency"],"backgroundTag":null,"analyzedSha":"0d85fdc91230885bca0a91df278312800a48b727","analyzedAt":"2026-08-12T16:24:28.056Z","schemaVersion":2},"datasetVersion":"2026-08-12T18:17:37.767Z"}