Cursor Rules Library

What's in this pack

Cursor's Project Rules (.mdc files in .cursor/rules/) are the highest-leverage way to lock in style, architecture, and process expectations for a codebase. The default Cursor setup ships with no rules; teams either write theirs from scratch (slow, drifting) or paste the same boilerplate across every project (no shared maintenance). This pack collects the nine .mdc packs that cover 80% of what most teams actually want, plus an MDC generator that builds custom rules from your existing docs.

Why this matters

The Cursor agent without rules is a generalist. With rules, it's an opinionated teammate that already knows your stack, your idioms, and your guardrails. Three concrete wins teams report after installing this pack:

1. Onboarding goes from days to hours. A new engineer's Cmd-K produces code that already looks like the rest of the codebase, because Cursor is reading the same conventions doc the human reads on day one.
2. Review fatigue drops. Reviewers stop catching the same five style/architecture nits on every PR — the rules catch them at generation time. Reviews focus on logic and trade-offs, where humans add the most value.
3. AI overreach is bounded. The Devin engineer-mode rules establish "plan first, edit minimally, don't refactor unrelated code." This single rule prevents the most common Cursor failure: a one-line bug fix that turns into 200 lines of unsolicited "improvements."

Install in one command

# Install the entire pack into the current project
tokrepo install pack/cursor-rules-library

# Or pick a single language/framework
tokrepo install python-cursor-rules
tokrepo install react-cursor-rules
tokrepo install devin-engineer-mode

The TokRepo CLI writes the .mdc files to .cursor/rules/ in your repo. Cursor picks them up on the next prompt — no restart required. To regenerate rules from your existing docs:

tokrepo run mdc-generator --input ./docs --output ./.cursor/rules/project.mdc

Common pitfalls

• One mega-rule that covers everything. Cursor loads matching rules per request based on glob scoping. A single 2000-line .mdc blows your context budget on every prompt. Split by domain: language rules in one file, architecture in another, security in a third.
• No glob scoping. A backend rule that fires on every frontend file wastes tokens and confuses the agent. Use globs: in the frontmatter to scope rules to **/*.py, app/**/*.tsx, etc.
• Forgetting Devin engineer-mode for non-Devin tools. This rule isn't actually Devin-specific — it's a generic "behave like a senior engineer" operating manual. It works just as well in Cursor, Claude Code, Codex CLI, and Cline (use the converter from the Skills Ecosystem pack).
• Treating rules as static. When your stack evolves, the rules need to evolve. Version-control the .cursor/rules/ directory and review changes in PR like any other code. The MDC generator can re-emit rules when your docs change.
• Pasting code examples that drift from reality. A rule that says "use fooBar() for X" and your code uses bar_foo() is worse than no rule. Either keep examples minimal and abstract, or generate them from real code via the MDC generator.

When this pack alone isn't enough

If you use both Cursor and another AI tool (Claude Code, Codex CLI, etc.), authoring .mdc directly locks you into Cursor. The Skills Ecosystem pack lets you author once in the canonical skill format and emit .mdc for Cursor plus AGENTS.md for Codex CLI, subagents for Claude Code, etc. Use this Cursor Rules Library pack if you're Cursor-only; switch to skills if you're multi-tool.

For pure Cursor power-users: pair this pack with the AI Code Editor Showdown comparison to understand where Cursor wins and loses against Zed, Cody, Continue, Morphic, and OpenCode — useful for advocating Cursor internally or deciding when to switch.