AI Code Completion Customization: Stack-Specific Configuration

Generic AI code suggestions often miss project-specific conventions, causing developers to spend time refactoring output. The major AI coding tools support project-level config files that fix this: Cursor uses `.cursorrules` or `.mdc` files, GitHub Copilot reads `.github/copilot-instructions.md`, and Claude Code loads `CLAUDE.md`. The guide covers exact syntax for each format, explains how negative rules ('never use X') outperform positive ones, and provides a ready-to-use configuration library for React 19, Vue 3, Svelte 5, Next.js 14, Django REST Framework, Fastify/Prisma, Laravel 11, Rails 7, Spring Boot 3/Kotlin, Flutter, and React Native/Expo. It also covers how to measure config effectiveness via acceptance rates and CI pass rates, and how to iterate by converting repeated manual corrections into new rules.