Tutorial: Set Up Insomnia 5.0 for Testing Next.js 15 API Routes Insomnia 5.0 is a powerful, open-source API client that simplifies testing REST, GraphQL, and gRPC endpoints. When working with Next.js 15, which introduces performance improvements and enhanced App Router capabilities, validating your API routes is critical to ensuring reliable application behavior. This tutorial walks you through configuring Insomnia 5.0 to test Next.js 15 API routes end-to-end, from basic GET requests to authenticated endpoints. Prerequisites Node.js 18.17 or later installed (required for Next.js 15) Existing Next.js 15 project (or create one with npx create-next-app@latest ) Insomnia 5.0 downloaded from the official site Basic understanding of REST API concepts and Next.js App Router Step 1: Install and Launch Insomnia 5.0 After downloading the Insomnia 5.0 installer for your operating system (Windows, macOS, Linux), run the installation wizard and launch the application.…