Cursor AI Custom Prompts Configuration Guide

Configuration Methods Comparison

Method	Reliability	Complexity	Primary Failure Mode	Use Case
Project Rules (.mdc)	70%	High	Glob pattern syntax, metadata formatting	Team standards, complex rules
User Rules	70%	Medium	Conflicts with project rules	Personal preferences only
AGENTS.md	50%	Low	AI randomly ignores file	Simple project documentation
Rules for AI	Until restart	Low	Configuration wiped on restart	Testing and debugging

Critical Implementation Requirements

MDC File Format Specifications

• Location: .cursor/rules/ directory (manual creation required)
• Extension: .mdc files only
• Syntax: Case-sensitive YAML metadata header with triple-dash delimiters
• Critical: One syntax error breaks entire rule

Working Example:

---
description: React component standards
globs: ["src/components/**/*.tsx", "src/pages/**/*.tsx"]
alwaysApply: false
---

React component requirements:
- TypeScript interfaces only (no PropTypes)
- Functional components only
- Destructure props in function signature
- Include error boundaries

Context Degradation Patterns

• Failure Point: 50+ messages in conversation
• Symptom: AI ignores previously followed rules
• Solution: Start new chat session
• Prevention: Monitor conversation length

Memory Feature Trade-offs

• Requirement: Disable privacy mode (code sent to Cursor servers)
• Syntax: End statements with "Keep that in mind"
• Learning Time: ~1 week for consistent behavior
• Risk: Code privacy concerns

Production Configuration Strategy

Step 1: Project Rules Setup

# Manual directory creation (Command Palette is unreliable)
mkdir -p .cursor/rules

Base Rule Template:

---
description: Core development standards
globs: ["src/**/*.ts", "src/**/*.tsx"]
alwaysApply: false
---

Development Standards:
- Explicit imports (no import *)
- Descriptive variable names
- Comment complex logic only
- TypeScript strict mode

Step 2: User Rules (Personal Preferences Only)

Location: Settings → Rules for AI

Recommended Content:

Communication:
- Show working code without explanations
- Explain failures with fix instructions

Code Style:
- Explicit imports required
- Descriptive variable names
- Minimal comments

Step 3: Context Engineering Best Practices

• Avoid: @Notepad feature (gets out of sync)
• Use: Comment headers in key files
• Example:

// API Architecture:
// - All endpoints return { data, error }
// - Zod validation required
// - Global error handler
// - No async/await in React components

Troubleshooting Guide

Rules Not Working

1. Check conversation length (>50 messages = restart needed)
2. Validate MDC syntax (case-sensitive, exact formatting)
3. Verify active rules: Ask "What rules are you following?"
4. Check Agent sidebar for active rule indicators

Common Syntax Errors

• alwaysApply: False → alwaysApply: false (case sensitive)
• Missing dashes in metadata header
• Incorrect YAML indentation
• Invalid glob patterns

Rule Conflicts

• Problem: Multiple rule types firing simultaneously
• Symptom: Contradictory AI behavior
• Solution: Keep rule layers consistent
• Example: User Rule "be concise" + Project Rule "explain everything" = novel-length responses

Auto-Run Mode Configuration

Safe Commands (Allowed)

npm run build
npm test
npm run lint
tsc --noEmit
eslint src/

Dangerous Commands (Denied)

npm install
rm -rf node_modules
git push --force
sudo *
# Long-running tests (>5 minutes)

Critical Warning

Auto-Run cannot be interrupted once started. Only allow commands you can safely wait for completion.

Model-Specific Behavior

Claude 3.5 Sonnet

• Rule Adherence: Excellent (95%)
• Speed: Slow
• Use Case: Complex refactoring with detailed rules

GPT-4o

• Rule Adherence: Good (80%)
• Speed: Fast
• Use Case: Quick fixes, less strict rule requirements

GPT-4o Mini

• Rule Adherence: Fair (60%)
• Speed: Very fast
• Use Case: Simple tasks, treats rules as suggestions

o1-preview/o1-mini (Cursor 1.5)

• Rule Adherence: Excellent for complex interactions
• Speed: Slow
• Cost: High
• Use Case: Conflicting rules resolution

Resource Requirements

Time Investment

• Initial Setup: 30 minutes
• Advanced Configuration: 2-4 hours
• Maintenance: 15 minutes per month
• Learning Curve: 1-2 weeks for complex rules

Expertise Requirements

• Basic: Understanding of glob patterns
• Intermediate: YAML syntax knowledge
• Advanced: Model behavior understanding

Migration Path

From .cursorrules to Project Rules

• Status: .cursorrules deprecated but still functional
• Recommendation: Migrate only if current setup has issues
• Complexity: High (new syntax, different behavior)

Breaking Points and Failure Modes

Critical Failures

1. Context Degradation: AI stops following rules after long conversations
2. Syntax Errors: Single character mistakes break entire rule
3. Glob Pattern Failures: Incorrect patterns = rules never trigger
4. Memory Conflicts: Multiple rule types creating contradictions

Performance Impact

• Nested Rules: Slow debugging, unpredictable behavior
• File References: Often fail silently (@filename syntax unreliable)
• Complex Configurations: Maintenance overhead exceeds benefits

Essential Resources

Community Documentation

• Awesome Cursorrules Repository: Working examples
• Cursor.Directory: Searchable rule database
• MDC Best Practices: Comprehensive MDC guide

Official Support

• Cursor Documentation: Minimal official docs
• Cursor Forum: Community support
• GitHub Issues: Bug reports

Support Quality

• Official Documentation: Poor (community-driven alternatives required)
• Forum Support: Good (active community)
• Discord: Excellent (real-time help)

Decision Criteria

When to Use Advanced Configuration

• Yes: Repetitive rule requests across multiple conversations
• Yes: Team standardization requirements
• No: More time configuring than coding
• No: Simple, one-off projects

Cost-Benefit Analysis

• High Value: Basic project rules (30 min setup, ongoing benefits)
• Medium Value: Memory features (privacy trade-off)
• Low Value: Nested rule hierarchies (high maintenance)
• Negative Value: Over-engineered configurations (productivity loss)

Security Considerations

Privacy Mode Implications

• Default: Code stays local
• Memory Features: Code sent to Cursor servers
• Risk: Intellectual property exposure
• Mitigation: Separate configurations for sensitive projects