# HP6001: Mismatch hidden by suppressHydrationWarning > HP6001 (suppressed-mismatch) lists a server and client difference hidden by suppressHydrationWarning. When it is fine, and when it hides a real bug. Source: https://hydration.jscrate.dev/docs/issues/hp6001 Last updated: 2026-09-18 HP6001 (`suppressed-mismatch`) means the server and client values differ on an element marked with `suppressHydrationWarning`. React does not report the difference and keeps the server value. That is fine for intentional differences such as timestamps or a theme class; check that this one is, and keep the attribute on the smallest element possible. | | | | --- | --- | | Code | `HP6001` | | Name | `suppressed-mismatch` | | Default severity | Info | | Group | suppressHydrationWarning audit | | What it means | The server and client values differ on an element marked with suppressHydrationWarning. React keeps the server value. | ## What the HP6001 suppressed mismatch finding means `suppressHydrationWarning` silences React for one element's own text and attributes. hydration-proof still compares them, and lists every difference it hides, so you know what you are suppressing: ```text Server rendered "10:04:31", the client rendered "10:04:33" (suppressHydrationWarning). ``` It finds them in three places: - the text and attributes React renders for the marked element, compared with the server HTML; - text that React 18 replaced during hydration on a marked element; - changes a script made to a marked element before hydration, such as a theme script that sets a class on `` (this would otherwise be [HP4001](https://hydration.jscrate.dev/docs/issues/hp4001)). The cause is always [intentional difference](https://hydration.jscrate.dev/docs/causes/suppressed). ### When HP6001 is a warning The finding is info when the hidden difference looks intentional: the time, a timezone, a locale, a random value, the theme or a browser extension. When it looks like something else, such as browser storage, a browser-only API or different data, it is raised to a warning with this note: ```text suppressHydrationWarning hides a difference that does not look intentional (localStorage / sessionStorage read during render). ``` That usually means the attribute was added to make an error go away, and users see the wrong server value until the next render. ## Likely causes - A timestamp or relative time rendered on both sides, the classic use of the attribute (see [time](https://hydration.jscrate.dev/docs/causes/time)). - A theme script that sets a class or `data-theme` on `` before React hydrates (see [theme](https://hydration.jscrate.dev/docs/causes/theme)). - A value read from storage or `window` and hidden instead of fixed. ## How to fix it This is fine if the difference is intentional (timestamps, for example). Keep `suppressHydrationWarning` on the smallest element possible. The two patterns it exists for: ```tsx title="app/layout.tsx" // A theme script changes the class on before hydration export default function RootLayout({ children, }: { children: React.ReactNode; }) { return ( {children} ); } ``` ```tsx title="components/updated-at.tsx" // The time on the element itself, not on a wrapper export function UpdatedAt({ iso }: { iso: string }) { return ( {new Date(iso).toLocaleTimeString()} ); } ``` When the finding is a warning, fix the cause instead: read storage and browser APIs in an effect, or send the server's data to the client. Then remove the attribute. ## Configure the audit `checks.suppressedWarnings` controls the whole HP6xxx group: | Value | Effect | | ------------------ | --------------------------------------------------------------------------------- | | `'info'` (default) | Lists hidden differences as HP6001 | | `'strict'` | Also reports suppression with nothing to suppress ([HP6003](https://hydration.jscrate.dev/docs/issues/hp6003)) | | `'off'` | Drops HP6xxx findings from the report | Info findings do not fail the run and are not printed in the terminal list; the HTML and JSON reports show them. To silence a single one, see [ignoring findings](https://hydration.jscrate.dev/docs/ignoring). ## Catch it with ESLint [`audit-suppress-hydration-warning`](https://hydration.jscrate.dev/docs/rules/audit-suppress-hydration-warning) reports the attribute where it has no effect or covers more than one element's text, and with `reportAll: true` every use. ## Related - [When suppressHydrationWarning is safe](https://hydration.jscrate.dev/docs/guides/suppresshydrationwarning) - [HP6002: suppression cannot hide a structural difference](https://hydration.jscrate.dev/docs/issues/hp6002) - [HP6003: suppressHydrationWarning with nothing to suppress](https://hydration.jscrate.dev/docs/issues/hp6003) - [Theme preference and dark mode](https://hydration.jscrate.dev/docs/causes/theme) - [The audit-suppress-hydration-warning rule](https://hydration.jscrate.dev/docs/rules/audit-suppress-hydration-warning)