How to Fix
Bolt API Route Errors

Why Bolt API Routes Break

Bolt generates frontend and backend simultaneously. The challenge is that the frontend and backend code are generated in the same conversation — they start in sync, but as you add features, they drift apart. The frontend calls endpoints that no longer exist, or endpoints that return data in a different format.

This is the most common cause of API failures in Bolt apps: the frontend and backend fall out of sync.

Error: API Route Returns 404

The frontend calls /api/users but the server returns 404. The file exists but something is wrong with the route.

Common causes: The route file is in the wrong location (Next.js App Router requires specific file naming), the HTTP method is not exported (GET, POST, etc.), or the file has a TypeScript error that prevents it from loading.

Fix: Verify the file is at app/api/... with the correct filename. Add export async function GET() or the appropriate method. Run the dev server and test the route directly with curl.

Error: API Route Returns 500

The route exists but returns a 500 Internal Server Error. This usually means an unhandled exception in the handler.

Fix: Wrap your handler in try-catch. Return proper error responses with status codes. Check server logs for the actual error. Common culprits: database connection failures, missing environment variables, and unhandled promise rejections.

Error: CORS Errors

Browser console shows CORS errors — the frontend cannot talk to the backend.

Fix: Add CORS headers to your API routes. For Next.js App Router, create a middleware or add headers to your next.config.js. The simplest fix is export const dynamic = 'force-dynamic' with proper CORS headers returned from each handler.

Getting Help

API issues can be tricky to debug without the right tools. We have fixed hundreds of Bolt API route errors.