vercel/next.js · error

Mangling is disabled. Note: This may affect performance and

Error message

Mangling is disabled. Note: This may affect performance and should only be used for debugging purposes.

What it means

Informational warning printed by next-build at startup when identifier mangling is disabled (the default unless --turbopack-mangle or equivalent is used, or when explicitly turned off). It means symbols in the production bundle keep their original names, which increases bundle size and can reduce runtime performance; it is intended only for debugging production builds with readable stack traces.

Source

Thrown at packages/next/src/cli/next-build.ts:74

    experimentalUploadTrace,
    debugBuildPaths,
  } = options

  let traceUploadUrl: string | undefined
  if (experimentalUploadTrace && !process.env.NEXT_TRACE_UPLOAD_DISABLED) {
    traceUploadUrl = experimentalUploadTrace
  }

  const bundler = parseBundlerArgs(options)

  if (experimentalAnalyze && bundler !== Bundler.Turbopack) {
    printAndExit(
      '--experimental-analyze is only compatible with the Turbopack bundler.'
    )
  }

  if (!mangling) {
    warn(
      `Mangling is disabled. ${italic('Note: This may affect performance and should only be used for debugging purposes.')}`
    )
  }

  if (profile) {
    warn(
      `Profiling is enabled. ${italic('Note: This may affect performance.')}`
    )
  }

  if (debugPrerender) {
    warn(
      `Prerendering is running in debug mode with NODE_ENV='development'. ${italic(
        'This will affect performance and should not be used for production.'
      )}`
    )
  }

View on GitHub (pinned to 0eb3775416)

Solutions

1. Remove the disable-mangling flag for normal builds; keep it only for debugging sessions.

When it happens

Trigger: Thrown at packages/next/src/cli/next-build.ts:74 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of vercel/next.js@0eb3775416 (2026-08-19). Data as JSON: /api/errors/e7145574caf24319. Report an issue: GitHub.