What it does

This repo collects Markdown-based .mdc files—Cursor’s “Project Rules” format—that you drop into .cursor/rules/. Each file tells the AI editor how to behave for a specific stack: Next.js 15 with Supabase security gotchas, Svelte 5 vs Svelte 4 migration patterns, Shopify Liquid theme constraints, and dozens more. Think of it as a shared brain for preventing Cursor from generating the wrong useEffect or leaking Stripe keys into client code.

The interesting bit

The value isn’t the format—.mdc is just Markdown with frontmatter—it’s the specificity. One Next.js 15 rule enumerates 27 architecture constraints (getSession vs getUser, synchronous params, missing RLS) that you’d otherwise correct manually, repeatedly. The repo turns tribal knowledge into copy-pasteable guardrails.

Key highlights

• 100+ rules across 13 categories: frontend frameworks, backend, mobile, games, CSS, state management, databases, testing, deployment, build tools, languages, security, documentation
• Heavy Next.js and React coverage, but also Solid.js, Qwik, Svelte, Astro, Angular, and niche stacks like Shopify Liquid or Semiotic data viz
• Some rules target specific AI workflows: “built for Cursor Agent and Claude Code”
• Community submissions; some rules are vendor-sponsored (CodeRabbit, Unblocked MCP, Warp)
• Modern .mdc format; older .cursorrules files appear to be deprecated

Caveats

• Quality and depth vary by rule; some are thin framework descriptions, others are dense security checklists
• README is mostly a directory; you can’t evaluate a rule without opening its .mdc file
• Sponsorship banners are prominent

Verdict

Worth bookmarking if you use Cursor heavily and tire of re-explaining your stack. Less useful if you want deep, battle-tested rules for every framework—some entries are starter templates dressed up as guardrails.