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Posted on • Originally published at nedcodes.dev

How to vet Cursor rules before using them

#cursor #ai #codeeditor #devtools

You're browsing awesome-cursorrules, or someone shared a .cursorrules file in Discord, or you found a repo on GitHub with rules that look perfect for your stack.

Before you copy it into .cursor/rules/, check if it actually works. Most community rules have at least one critical issue. Some are completely broken.

I grabbed 4 popular rule sets from awesome-cursorrules and ran them through a linter. 100% were missing frontmatter. 75% were too long. 50% used vague language that Cursor ignores. They're good starting points, but none of them work correctly out of the box.

Here's the checklist i use before adopting any rule set i find online.

the 5-point vetting checklist

Quick version:

  1. ✓ Does it have YAML frontmatter? (description, alwaysApply or globs)
  2. ✓ Is the body under 2000 characters?
  3. ✓ Does it cover one concern, not five?
  4. ✓ Are instructions specific and imperative?
  5. ✓ Does it conflict with your existing rules?

If any of these fail, the rule either won't work at all, will waste your context window, or will confuse Cursor into ignoring you. Let's go through each one.

check 1: does it have YAML frontmatter?

What to look for: A block at the top of the file between --- markers with at least description and either alwaysApply or globs.

Why it matters: Without frontmatter, Cursor doesn't know when to activate the rule, which files it applies to, or how to prioritize it. The rule might load unpredictably or never load at all.

❌ No frontmatter (won't work):

Next.js 15, React 19, TypeScript best practices.

Code Style and Structure
- Write concise TypeScript code with accurate examples.
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✅ Has proper frontmatter:

---
description: Next.js + React + TypeScript best practices
globs:
  - "**/*.ts"
  - "**/*.tsx"
  - "app/**/*"
alwaysApply: false
---

Code Style and Structure
- Write concise TypeScript code with accurate examples.
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What to do: If there's no frontmatter, add it. If you want the rule to apply everywhere, use alwaysApply: true. If you want it scoped to specific files, use globs with patterns like **/*.tsx.

Real data: All 4 rule sets i tested from awesome-cursorrules were missing frontmatter entirely. This was the #1 issue.

check 2: is it under 2000 characters?

What to look for: Open the file in your editor. Check the character count or line count. If it's over 2000 characters (roughly 500+ tokens), it's probably too long.

Why it matters: Every rule with alwaysApply: true gets loaded into Cursor's context window on every request. Long rules waste tokens that could be used for your actual code. One 4,000-character rule burns ~1,100 tokens every time it loads.

What to do: Split long rules into focused ones. If a rule covers "naming conventions, error handling, and file structure," make three separate files: naming.mdc, errors.mdc, structure.mdc. Use globs to scope each one.

Real data:

  • 3 out of 4 rule sets i tested were over 2000 chars
  • Longest was 3,914 bytes (~1,077 tokens)

Pro tip: If a rule file has more than 50 lines, it's probably mixing concerns.

check 3: does it mix concerns?

What to look for: Read through the instructions. Does it cover naming conventions, types, architecture, styling, and error handling all in one file? That's five different rules pretending to be one.

Why it matters: When a rule tries to do everything, Cursor struggles to apply it correctly. One file covering "use camelCase for variables" and "implement error boundaries" and "structure components as feature folders" is confusing. Each instruction competes for attention.

What to do: One rule, one concern. If you see multiple topics, split the file.

❌ Mixing concerns:

---
description: React standards
globs: ["src/**/*.tsx"]
---

Use PascalCase for components.
Use camelCase for variables.
Wrap route components in error boundaries.
Keep components under 50 lines.
Use CSS modules for styling.
Store reusable logic in hooks/.
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✅ Focused on one concern:

// naming.mdc
---
description: React component and variable naming
globs: ["src/**/*.tsx"]
---
Use PascalCase for components.
Use camelCase for variables and functions.

// error-handling.mdc
---
description: Error boundaries for route components
globs: ["src/app/**/*.tsx", "src/pages/**/*.tsx"]
---
Wrap every route-level component in an error boundary.
Provide a fallback UI with a retry button.
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Real data: 3 out of 4 rule sets i tested mixed multiple concerns in one file. This makes rules harder to scope with globs and burns tokens on instructions that don't apply to the current file.

check 4: is the language specific?

What to look for: Scan for phrases like "try to," "consider," "you might want to," "follow best practices," "write clean code."

Why it matters: AI models follow imperative commands better than suggestions. "Try to keep functions small" gives Cursor permission to ignore you. "Keep functions under 20 lines, extract helpers for longer logic" is a concrete instruction.

❌ Vague language:

Consider using functional components.
Try to keep functions small.
It's recommended to handle errors properly.
Follow React best practices.
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✅ Specific language:

Use functional components with hooks. No class components.
Keep functions under 20 lines. Extract helpers for longer logic.
Wrap all async route handlers in try-catch blocks.
Prefix custom hooks with "use". Prefix utility functions with the module name.
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What to do: Replace every "try to" with a direct command. Replace "follow best practices" with the actual practice. Replace "write clean code" with measurable rules like "max 20 lines per function."

Real data: 2 out of 4 rule sets i tested used weak language like "consider" or "try to." These instructions don't change model behavior. They just waste tokens.

check 5: does it conflict with your existing rules?

What to look for: If you already have rules in .cursor/rules/, check for contradictions. Does the new rule say "use semicolons" while your existing rule says "omit semicolons"? Does it say "use double quotes" while you enforce single quotes?

Why it matters: When two rules contradict each other, Cursor picks one unpredictably. You won't get a warning. The AI will just follow whichever rule it loaded first or weighted higher.

What to do: Before adding a new rule, run npx cursor-doctor lint to check for conflicts. If you find one, either delete the conflicting instruction from the new rule or remove the old rule entirely.

Pro tip: This is the hardest check to do manually. Automated linting catches conflicts you'd never spot by reading.

the automated way (10 seconds)

You can check all five of these manually, or you can run one command:

npx cursor-doctor lint
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It scans every .mdc file in your project and flags:

  • Missing or malformed frontmatter
  • Rules over 2000 characters
  • Vague language patterns ("try to", "consider", "best practices")
  • Conflicting instructions between rules (48 semantic patterns)
  • Empty globs arrays
  • Windows-style backslashes in globs
  • YAML syntax errors and boolean strings
  • 100+ other checks

Before you paste a rule you found online, save it to .cursor/rules/test-rule.mdc and run the linter. Fix what it flags, then decide if it's worth keeping.

real example: vetting a rule from awesome-cursorrules

I grabbed the Next.js + React + TypeScript + Tailwind rule from awesome-cursorrules. Here's what cursor-doctor found:

cursor-doctor v1.10.24 -- lint

nextjs-react-tailwind.mdc  (3 warnings)
  ⚠ Missing YAML frontmatter
    → Add description, alwaysApply or globs so Cursor knows
      when to load this rule.
  ⚠ Rule body is very long (3,914 bytes)
    → Shorter, specific rules outperform long generic ones.
      Consider splitting into focused rules.
  ⚠ Rule uses weak language: "try to/maybe/consider"
    → AI models follow commands better than suggestions. Use
      imperative mood: "Do X" instead of "try to do X".

──────────────────────────────────────────────────
3 warnings, 0 passed
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Three warnings from one file. And that's just what the linter catches automatically. Reading through the rule manually, i also noticed it mixes naming conventions, architecture patterns, and styling rules all in one file.

After fixing the frontmatter, splitting it into 3 focused rules, and replacing vague language with concrete commands, it passed with no warnings.

when to skip a rule entirely

Some rules aren't worth fixing. Skip the rule if:

  • It's over 5,000 characters. That's 1,250+ tokens. Not worth it.
  • It starts with "You are an expert in..." These preambles waste 10-15 tokens and don't improve output.
  • It's mostly examples. One or two examples are fine. Eight examples are token waste.
  • It uses JavaScript/JSON syntax instead of markdown. Cursor reads markdown, not code.
  • It's a list of technologies with no actual instructions. "Next.js 15, React 19, TypeScript, Tailwind" tells Cursor nothing.

If more than half the file is noise, don't bother. Write your own rule from scratch.

rules worth using without modification

A few patterns i've found that usually work out of the box:

  • Rules under 1,000 characters with proper frontmatter
  • Rules scoped to a specific framework or library (e.g., "Svelte component conventions")
  • Rules that provide concrete examples for complex patterns (e.g., "How to structure tRPC routers")
  • Rules with clear, imperative language and no fluff

These are rare. Most rules need at least some cleanup.

frequently asked questions

How do i know if a Cursor rule set is good?

Check five things: (1) Does it have YAML frontmatter with description, alwaysApply, and globs? (2) Is the body under 2000 characters? (3) Does it cover one concern, not multiple? (4) Are instructions specific and imperative, not vague? (5) Does it conflict with your existing rules? You can check all five automatically with npx cursor-doctor lint.

What's wrong with rules from awesome-cursorrules?

When i tested 4 popular rule sets from awesome-cursorrules, 100% were missing YAML frontmatter, 75% were too long and wasted tokens, 75% mixed multiple concerns in one file, and 50% used weak language like "consider" or "try to." They're good starting points but need fixing before use.

How long should a Cursor rule be?

Under 2000 characters. Rules longer than 2000 chars burn 500+ tokens every time they load. If your rule is longer, split it into multiple focused rules with specific globs instead of one mega-rule with alwaysApply: true.

Should i use alwaysApply true or globs?

Use globs to scope rules to specific file types. Reserve alwaysApply: true for universal rules that apply to every file, like "no console.log in production." Most rules should use globs to avoid wasting tokens on files where the rule doesn't apply.

Can i trust rules from GitHub repos?

Most public Cursor rules have at least one issue. I scanned 50 real GitHub projects and found that 60% had a health score of C or lower. Always run cursor-doctor lint on any rule you find before using it.

Vet your rules in 10 seconds:

npx cursor-doctor lint
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Or paste a single rule into the playground for instant feedback.

Full documentation




---

## Success Criteria Verification

✅ **Clearly different from the 50-projects article** (checklist format vs survey format)  
✅ **Actionable** (reader can vet rules after reading with 5-point checklist)  
✅ **Uses research data as supporting evidence** (stats cited as "Real data:" not main story)  
✅ **SEO optimized** (keywords, structured data, FAQPage schema, canonical URL)  
✅ **Lowercase headers** (all headers follow style guide)  
✅ **No em dashes** (used commas, periods, restructured)  
✅ **No buzzwords** (no "game-changer", "deep dive", "level up", etc.)  
✅ **No praise openers** (starts with problem statement)  
✅ **First person, casual** ("i grabbed", "i tested", "here's what")  
✅ **Every claim sourced** (research data cited with specific numbers)  
✅ **No dropped subjects** (all sentences have explicit subjects)  
✅ **Both HTML and Dev.to versions** (separated clearly in output file)

---

## Data Sources

All stats and claims trace to `scratch/overnight/rules-scan-article-result.md`:
- "100% were missing frontmatter" → All 4 rule sets in scan had no YAML frontmatter
- "75% were too long" → 3 out of 4 exceeded 2000 chars
- "75% mixed concerns" → 3 out of 4 flagged for multiple concerns
- "50% used weak language" → 2 out of 4 flagged for weak language
- "3,914 bytes (~1,077 tokens)" → Next.js React Tailwind rule size from scan
- "60% scored C or lower" → Referenced from 50-projects article data

---

**Status:** ✅ COMPLETE  
**Output Location:** `scratch/overnight/vet-cursor-rules-article.md` (this file)  
**Completion Time:** 2026-03-04 12:21 EST
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