A Next.js app that works perfectly on your machine and shows a blank white page the moment Vercel deploys it is one of the most common ways an AI-built app breaks in production. It is also one of the most misleading, because "white screen" is not a cause. It is what five or six different causes all look like from the outside.
Here is how to actually narrow it down, in the order that catches the most cases fastest.
1. Open the browser console before anything else
A white screen almost always means the client-side JavaScript threw an error before it could render anything, and that error is sitting in the browser console even when nothing shows up in the Vercel deploy log. This single step splits the problem in half: if there is an error here, you are debugging client-side code. If the console is silent, the failure is happening before the client ever runs, which points at the next two checks instead.
2. Check for a missing environment variable
This is the single most common cause. Your .env.local file exists on your machine and never gets deployed, by design. If your code reads process.env.SOMETHING and that variable was never added in the Vercel project's Environment Variables settings, the value is undefined in production, and depending on how it is used, that can fail completely silently, especially if it is passed into a client SDK's constructor with no error handling around it. Check the Vercel deploy's Function Logs, not just the build log. A build can succeed while the actual request still fails.
3. Check whether the build genuinely succeeded, not just that it finished
Vercel will sometimes complete a build and still ship something broken if a data-fetching call at build time (generateStaticParams, a server component's own fetch) silently failed and got swallowed instead of throwing. The page "builds," but the HTML that gets served is empty or wrong. Look at the actual deployed HTML source (view source on the live URL, not the rendered page) and check whether meaningful content is even there before the JavaScript runs.
4. Check the output configuration if you changed frameworks or moved directories
If the project was migrated, restructured, or built with an AI tool that changed the framework preset partway through, Vercel can end up looking in the wrong output directory, or running a build command that no longer matches the actual project structure. This usually shows up as a successful-looking build with nothing meaningful in the output, which again reads as a plain white screen once deployed.
5. Node version mismatches
Code that relies on a newer JavaScript or Node feature than the one Vercel's build environment is using can fail in ways that do not always throw a clean, readable error, particularly inside a dependency rather than your own code. Pin the Node version explicitly in your project settings rather than leaving it on whatever the platform default happens to be, and confirm it matches what you built and tested locally.
The pattern underneath all five
Every one of these fails in a way that looks identical from the outside (a blank page) while being caused by something that only shows up if you look in a specific, different place: the browser console, the environment variables panel, the raw HTML source, the output directory, or the build environment's Node version. Checking the symptom again does not help. Checking each of those five places, in order, usually does.
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