vercel/next.js · error · Error

Taint can only be used with the taint flag.

Error message

Taint can only be used with the taint flag.

What it means

Thrown by the notImplemented() stub that backs taintObjectReference() and taintUniqueValue() when the experimental React flag (__NEXT_EXPERIMENTAL_REACT) is not enabled. React's experimental_taintObjectReference / experimental_taintUniqueValue are only wired in under that flag; without it the taint APIs are inert stubs that error on use. Taint APIs help prevent leaking sensitive objects/values to the client.

Source

Thrown at packages/next/src/server/app-render/rsc/taint.ts:13

/*

Files in the rsc directory are meant to be packaged as part of the RSC graph using next-app-loader.

*/

import * as React from 'react'

type Reference = object
type TaintableUniqueValue = string | bigint | ArrayBufferView

function notImplemented() {
  throw new Error('Taint can only be used with the taint flag.')
}

export const taintObjectReference: (
  message: string | undefined,
  object: Reference
) => void = process.env.__NEXT_EXPERIMENTAL_REACT
  ? // @ts-ignore
    React.experimental_taintObjectReference
  : notImplemented
export const taintUniqueValue: (
  message: string | undefined,
  lifetime: Reference,
  value: TaintableUniqueValue
) => void = process.env.__NEXT_EXPERIMENTAL_REACT
  ? // @ts-ignore
    React.experimental_taintUniqueValue
  : notImplemented

View on GitHub (pinned to 0ae8c72462)

Solutions

1. Enable experimental React by setting __NEXT_EXPERIMENTAL_REACT=1 (or the project's documented experimental flag mechanism) if you truly need taint.
2. If taint is optional, guard its usage behind a feature check and avoid calling it when the flag is off.
3. Confirm your React/Next.js versions support the taint APIs before relying on them.
4. Remove the taint calls if you do not need the experimental protection.

Example fix

// before
// import { taintObjectReference } from 'next/dist/.../taint'
// taintObjectReference('secret', user) // throws without flag

// after: enable experimental react
// __NEXT_EXPERIMENTAL_REACT=1 next build

// Only call taint when the experimental flag is active.
const TAINT_ENABLED = process.env.__NEXT_EXPERIMENTAL_REACT === '1' || !!process.env.__NEXT_EXPERIMENTAL_REACT
if (TAINT_ENABLED) taintObjectReference('secret', obj)

function isTaintAvailable(): boolean {
  return Boolean(process.env.__NEXT_EXPERIMENTAL_REACT)
}

When it happens

Trigger: Application code imports and calls experimental_taintObjectReference or experimental_taintUniqueValue (the Next.js re-exports taintObjectReference/taintUniqueValue) while __NEXT_EXPERIMENTAL_REACT is falsy. The ternary at taint.ts:19/27 selects notImplemented, which throws on invocation.

Common situations: Using React's experimental taint API in a project without enabling experimental React; a tutorial/library that assumes the flag is set; building a security feature (preventing secrets from reaching client bundles) without the required experimental channel.

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AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/f37b7b8a9299f42f. Report an issue: GitHub.