Writing Effective Prompts

5.1: The Prompt Formula

Every effective prompt follows this structure:

[CONTEXT] + [TASK] + [CONSTRAINTS] + [OUTPUT FORMAT]

Example:

CONTEXT:     "We have a Next.js 14 app with Prisma and PostgreSQL."
TASK:        "Add rate limiting to the /api/auth endpoints."
CONSTRAINTS: "Use Redis. Max 5 attempts per minute per IP. No external libraries."
OUTPUT:      "Provide the middleware code and explain the approach."

This is called the context sandwich: what exists, what you want, and what the limits are.

5.2: The Context Sandwich

The most reliable prompt pattern for any task:

[What exists] + [What you want] + [Constraints]

Bad prompt:

Add authentication

Good prompt:

We have a Next.js app with Prisma (exists).
Add email/password auth using NextAuth.js (want).
Use the existing User model. No OAuth for now (constraints).

The bad prompt gives AI zero context about your stack, existing patterns, or boundaries. It will guess -- and guess wrong.

5.3: The Incremental Build Pattern

Never ask for everything at once. Build in small, reviewable steps:

Step 1: "Create the database schema for user profiles"
        -> Review, approve

Step 2: "Write the API endpoints for CRUD operations on profiles"
        -> Review, approve

Step 3: "Build the frontend form for editing profiles"
        -> Review, approve

Each step is small enough to review, test, and catch mistakes before they compound.

5.4: The Reference Pattern

Instead of describing what you want, point AI at existing code:

Create a ProductService following the exact pattern in
src/services/UserService.ts.

Same error handling, same return types, same validation approach.

This works better than describing the pattern because AI can see the actual implementation, not your description of it.

In Cursor, use @filename to bring files directly into context.

5.5: The Constraint Frame

Constrain what AI should NOT do. This prevents the most common AI mistakes:

Requirements:
- No new dependencies
- No changes to the database schema
- Keep the existing API contract
- Under 50 lines
- Follow the pattern in AuthService.ts

Without constraints, AI will:

• Add unnecessary packages
• Over-engineer with abstractions
• Change things outside your scope
• Write 200 lines when 20 would work

5.6: Anti-Pattern Prompts

Things that never work well:

5.7: Key Phrases That Work