5 .cursorrules Antipatterns Killing Your AI Productivity

A developer identified five common antipatterns in `.cursorrules` files that reduce AI coding productivity, including monolithic rule files that waste context budget and vague instructions like "write clean code" that fail to enforce specific behaviors. The fix involves splitting rules into scoped files per directory, writing automatable constraints with concrete failure conditions, and maintaining a single authoritative source of truth to prevent contradictions between tools like Cursor and Claude Code.

Your .cursorrules file is probably not working the way you think it is. Not because Cursor is broken — but because most .cursorrules setups make the same five mistakes. Here is what they are and how to fix them. The most common .cursorrules antipattern is the monolith: one file at the project root, 300 lines long, covering TypeScript conventions AND API auth patterns AND deployment notes AND "always write clean code." The problem: Cursor loads this file into every context, regardless of what you are editing. When you are fixing a CSS bug, your SQL query rules are burning token budget for nothing. When context gets long, older rules get compressed out — which means your most important constraints are the ones most likely to disappear. Fix: Split into scoped rule files. .cursorrules 50 lines: project overview, stack, non-negotiables src/api/.cursorrules Auth patterns, error format, rate limiting src/components/.cursorrules Component conventions, state patterns scripts/.cursorrules Env handling, idempotency, logging Each file loads only when files in that directory are open. Your total in-context rule budget stays tight. "Write clean, readable code." "Keep functions small." "Follow best practices." These are not rules. They are aspirations. The AI already knows what "best practices" means — and it will apply its own interpretation, not yours. Rules need to be specific enough to fail. If you cannot imagine a concrete code sample that violates the rule, the rule is too vague to enforce. Vague: "Handle errors properly." Specific: "All async functions must have a try/catch. Errors must be logged via logger.error before rethrowing. Never swallow errors silently." Vague: "Use descriptive variable names." Specific: "Boolean variables must start with is , has , should , or can . No single-letter names outside of loop indices." The second versions are automatable. The first versions are vibes. The AI does not know your project layout unless you tell it. This leads to imports from wrong paths, new files dropped in wrong directories, and helper functions duplicated because the AI didn't know one already existed. Add a compact directory map early in your .cursorrules : Project structure: src/ api/ Express routes + middleware services/ Business logic no HTTP models/ Prisma schema types utils/ Pure functions, no side effects types/ Shared TypeScript interfaces tests/ Mirrors src/ structure scripts/ One-off automation, not imported by app Eight lines. Enough to save the AI from putting a database call in a route handler because it didn't know services/ exists. If your .cursorrules says "never use any types" but your codebase has 200 any type usages, the rule is fighting the existing code. The AI gets conflicting signals: the rule says one thing, the examples in the codebase say another. The examples usually win. Your rules should describe what the code already does, not what you wish it did. If there is a gap — you want to adopt a new pattern but your codebase isn't there yet — say so explicitly: Migration in progress: we are removing any types. New code must not use any . Existing any usages will be fixed incrementally. Do not add new any even when refactoring old code. This gives the AI a clear mandate without creating a contradiction. If you use Cursor + Claude Code, you end up with .cursorrules and CLAUDE.md saying the same things in slightly different ways. Then one gets updated and the other doesn't. Then they contradict each other. Then neither is trusted. The fix is a single authoritative source with tool-specific adaptations: CLAUDE.md it is the most structured format and is loaded by Claude Code as a system prompt prefix . .cursorrules import or reference the same core rules, adding only Cursor-specific formatting/behavior.For greenfield projects, starting with a production-configured starter that already has both files wired up correctly saves this setup cost entirely. The Vibe Coder Kit https://blncraft.gumroad.com/l/vibe-coder-kit includes 12 starters Next.js SaaS, Express + JWT, FastAPI, Discord Bot, and more where .cursorrules and CLAUDE.md are already synchronized and match the actual codebase structure. Read each rule and ask: "Could a developer violate this rule while genuinely trying to follow it?" If yes, the rule is too ambiguous. Make it specific enough that violations are unambiguous. Then count your lines. If your .cursorrules is over 100 lines, split it. If it is under 20, you probably have not captured your real conventions yet. Short. Specific. Scoped. Consistent with the codebase. Those four constraints will make your AI coding setup work the way the demos promise. BLN Craft builds developer tools for AI-native workflows. Find us at blncraft.com.