Errors, explained

8 error messages that stop AI-built projects, each with what it means, the usual causes, a prompt that makes your AI tool find the cause before it changes anything, and how to check the fix.

Every page lists the official documentation it is based on. If a service itself might be the problem, check whether it is down first.

• Vercel build failedCommand "npm run build" exited with 1Your build command failed on Vercel's build machine, so nothing new was deployed.
• Module not foundModule not found: Can't resolve '…'Your code imports a package or file that cannot be found at the name the import uses.
• Hydration failedHydration failed because the server rendered HTML didn't match the clientThe page React built in the browser came out different from the HTML the server sent.
• CORS errorNo 'Access-Control-Allow-Origin' header is present on the requested resourceThe browser blocked your page from reading another site's response, because that site did not allow your site to read it.
• Supabase row-level securitynew row violates row-level security policy for table "…"Row-level security is on for the table, and none of its policies allowed this insert or update.
• 401 Unauthorized from an API401 UnauthorizedThe API did not accept your credentials: the key was missing, wrong, or no longer valid.
• ENOENTENOENT: no such file or directoryNode.js was asked to open a file or folder that does not exist at that path.
• Cannot read properties of undefinedTypeError: Cannot read properties of undefined (reading '…')Your code read a property from something that was undefined at that moment.