hydration-proof vs react-hydration-overlay

If you are looking for a react-hydration-overlay alternative, hydration-proof covers the same need, the server and client HTML side by side, without code in your app. Builder.io's overlay wraps your app and shows a diff on the page when hydration fails. hydration-proof tests every route in a real browser, locally or in CI, in development and production builds.

At a glance

What Builder.io's overlay does well

Builder.io's hydration overlay is a small, focused tool:

• A whole-page diff. An injected script captures the server HTML before hydration. When a hydration error happens, the overlay compares it with the client HTML and shows the difference on top of the page.
• Simple setup for Next.js. Wrap the app in HydrationOverlay and add withHydrationOverlay to next.config.js; appRootSelector points it at main for the App Router. A webpack plugin covers other setups.
• Visual and immediate. You see the diff where the error happened, without leaving the browser.

It has about 8,000 weekly downloads on npm.

Where hydration-proof differs

• Nothing added to your app. The overlay is a dependency, a wrapper component and a build plugin, and its README says it "is not intended for production use". hydration-proof injects its runtime into the test browser only; your code and bundle do not change.
• Every route, in CI. The overlay reports the page you open. hydration-proof discovers routes and tests all of them, in every scenario you configure, and fails the build when it finds a problem.
• Production builds and silent mismatches. The overlay is for development builds, and React 19 production builds do not report attribute mismatches at all. hydration-proof tests production builds by default and compares every attribute with what React renders on the client, so it finds those too.
• Where the difference started. The overlay's README notes that because React re-renders the whole app after a hydration failure, its diff can show false positives, and that React's changes to inline style formatting (an added ;, different whitespace) can look like differences. hydration-proof gives every node an identity across its snapshots and compares attributes with the props React renders, so it reports the element where a difference started (how it works).
• A cause, not only a diff. Each finding has a stable issue code, the component and source line, and a likely cause with a confidence score.
• Frameworks beyond Next.js. The overlay's README lists Remix and Vite SSR support as still needed. hydration-proof detects React Router, Remix, Astro and Vite SSR apps, and works with any server through --url.

Switching to a react-hydration-overlay alternative

1. Remove the HydrationOverlay wrapper and the withHydrationOverlay plugin from next.config.js, then uninstall the package.

2. Install hydration-proof and run it once:

   npmpnpmyarnbun

   Copy

   npm install -D hydration-proof
   npx hydration-proof install
   npx hydration-proof test

3. For the same browse-and-see workflow, run npx hydration-proof dev. It opens the app with a hydration overlay that shows each page's findings, highlights the element and opens the source line in your editor (dev overlay).

Sources

As of September 2026:

• BuilderIO/hydration-overlay on GitHub: README, setup, beta status and known false positives; about 530 stars
• The package on npm: version 0.3.0, published October 2024; 7,963 downloads in the week of September 10–16, 2026
• hydration-proof: how it works

Related

• Next.js dev overlay compared
• The hydration-proof dev overlay
• Debugging hydration errors
• All comparisons
• Quick start