Resolving TypeError: Failed to parse URL in Next.js Server Components

Problem Statement

When developing with Next.js 13+ Server Components, you might encounter this error:

TypeError: Failed to parse URL from api/users

This error occurs specifically when making fetch() requests to relative API routes (/api/users) within Server Components or server-side functions.

The root cause lies in the execution environment difference:

1. In browser environments, fetch('/api/users') resolves relative to the current origin
2. In Node.js environments (where Server Components execute), fetch() requires absolute URLs
3. No valid context (like the current host) exists during server-side execution

Solutions

1. Use Environment Variables with Absolute URLs

Replace relative URLs with absolute paths using environment variables:

const getUsers = async () => {
  const BASE_URL = process.env.NEXT_PUBLIC_BASE_URL;
  const result = await fetch(`${BASE_URL}/api/users`, {
    method: 'GET'
  });
  
  if (result.ok) return result.json();
  return [];
};

Create or update your environment configuration files:

NEXT_PUBLIC_BASE_URL="http://localhost:3000"

NEXT_PUBLIC_BASE_URL="https://your-production-domain.com"

IMPORTANT

• Use NEXT_PUBLIC_ prefix to expose variables in browser and server contexts
• For Vercel deployments, use VERCEL_URL for preview environments:

NEXT_PUBLIC_BASE_URL="${VERCEL_URL ? `https://${VERCEL_URL}` : 'https://fallback-domain.com'}"

2. Avoid Internal API Calls in Server Components (Recommended)

Instead of making HTTP requests to your own API routes from Server Components:

// Directly access data sources
import db from '@/lib/db';

export default async function IndexPage() {
  const users = await db.user.findMany(); 
  return <h1>Users: {users.length}</h1>;
}

WHY THIS IS BETTER

1. Build-time reliability: Avoids fetching during static rendering
2. Performance optimization: Eliminates unnecessary HTTP overhead
3. Simplified architecture: Direct database access avoids API middleware

Additional Configuration Notes

For Vercel deployments, configure environment variables:

# Preview environments
NEXT_PUBLIC_BASE_URL="https://${VERCEL_URL}"

# Production
NEXT_PUBLIC_BASE_URL="https://your-domain.com"

Runtime Considerations

export const fetchWithBase = async (path) => {
  // Use conditional based on execution environment
  const base = typeof window === 'undefined' 
    ? process.env.NEXT_PUBLIC_BASE_URL 
    : '';
    
  const response = await fetch(`${base}${path}`);
  return response.json();
};

Key Takeaways

1. Server Components execute in Node.js where relative URLs are invalid
2. Environment variables provide the most flexible solution for absolute URLs
3. Direct data fetching from Server Components is preferred over internal API calls
4. Conditional base URLs help manage different execution environments

AVOID THIS COMMON MISTAKE

// This fails in Server Components:
const result = await fetch('/api/users');

For production scalability, ensure NEXT_PUBLIC_BASE_URL is properly configured across all environments (local, preview, production).