Optimized LLM Prompt Library for Web Development

Best Practices for Writing Effective LLM Prompts

Writing good prompts is an art. Here are some best practices to ensure your prompts yield high-quality, robust code results:

1. Be Specific and Clear: Clearly state what you want. Specify the programming language, libraries or frameworks, and the nature of the output. For example, instead of “Build a website”, prompt “Build a responsive single-page website with a header, three content sections, and a footer using HTML5 and CSS3.”
2. Provide Context and Requirements: Give background on the project (e.g., target environment like Replit, accessibility standards, or performance goals).
3. Define Roles or Perspectives: Ask the LLM to “act as a senior developer” or “an expert in web security” to influence the style and thoroughness of the response.
4. Include Examples or Reference Code: Provide small examples to guide the AI toward a consistent format (few-shot prompting).
5. State Desired Quality and Robustness: Use keywords like “production-ready”, “secure”, “optimized”, and “well-documented”.
6. Mention Environment or Deployment Details: For example, specify that the app should run on Replit using app.run(host="0.0.0.0", port=8080).
7. Iterate and Refine: Use feedback from the model’s output to adjust and clarify your prompt.
8. Consider Asking for Self-Review: Request the AI to review its code for errors or performance issues before finalizing the output.
9. Always Validate and Test: Ask for unit tests or example test cases along with the code.

Following these best practices will help you guide the AI to produce high-quality, production-ready code.

Prompt Library for Web Development Tasks

This library contains categorized prompts for frontend, backend, and debugging/optimization tasks.

Frontend Development Prompts

HTML & CSS

• Basic Page Structure:
  Prompt: “Generate an HTML5 page with a responsive layout. It should include a header with navigation links, a main content section with two columns, and a footer. Use semantic HTML elements and include placeholder text and images. Provide CSS for a mobile-first responsive design.”
• Form with Validation (Vanilla):
  Prompt: “Write the HTML and CSS for a contact form that collects name, email, and message. Add JavaScript to validate that the name and email are not empty and that the email is valid. Display error messages below the fields in red if validation fails.”
• Styling with Bootstrap 5:
  Prompt: “Using Bootstrap 5, create an HTML snippet for a centered card component that contains an image, a title, some text, and a button link. Ensure the card is responsive.”

  <div class="card mx-auto" style="max-width: 18rem;">
    <img src="..." class="card-img-top" alt="..."/>
    <div class="card-body">
      <h5 class="card-title">Card Title</h5>
      <p class="card-text">Some quick example text.</p>
      <a href="#" class="btn btn-primary">Go somewhere</a>
    </div>
  </div>
  

• Responsive Image Gallery (CSS Grid):
  Prompt: “Create an HTML/CSS image gallery that displays thumbnails in a grid (3 columns on desktop, 2 on tablet, 1 on mobile). On hover, overlay a caption on each image. Use CSS Grid and include comments explaining the responsive breakpoints.”

JavaScript & Frontend Frameworks

• Interactive Dropdown Menu (Vanilla JS):
  Prompt: “Implement a JavaScript function that toggles a dropdown menu when a button is clicked. Include the necessary HTML, CSS, and JavaScript. Ensure that clicking outside the menu or on a menu item closes it.”
• React Component – UserCard:
  Prompt: “Create a React functional component called UserCard that displays a user’s avatar, name, and bio. If the bio exceeds 100 characters, truncate it and add a ‘show more’ toggle using React Hooks.”

  import React, { useState } from 'react';
  
  const UserCard = ({ user }) => {
    const [expanded, setExpanded] = useState(false);
    const toggleBio = () => setExpanded(!expanded);
    const bio = expanded ? user.bio : user.bio.substring(0, 100) + (user.bio.length > 100 ? '...' : '');
  
    return (
      
  
        
        
  {user.name}
        
  {bio}
        {user.bio.length > 100 && (
          
            {expanded ? 'Show Less' : 'Show More'}
          
        )}
      
    );
  };
  
  export default UserCard;
  

• Next.js SPA Routing:
  Prompt: “Generate a simple Next.js application with two pages: index.js (Home) and about.js (About). Use the Next.js Link component for navigation and include a package.json that makes it ready to run on Replit.”
• Performance Optimization Advice (Frontend):
  Prompt: “The following code is slowing down a webpage due to 1000 DOM elements being added on load. Analyze the code, suggest performance improvements, and provide an updated snippet with comments explaining your changes.”

Backend Development Prompts

Python & Flask

• Basic Flask App:
  Prompt: “Create a Flask web application in Python with two routes: `/` returning a welcome HTML message and `/api/status` returning JSON `{'status': 'ok'}`. Use app.run(host='0.0.0.0', port=8080) for Replit deployment and include explanatory comments.”

  from flask import Flask, jsonify
  
  app = Flask(__name__)
  
  @app.route('/')
  def home():
      return "<h1>Welcome to the Flask App</h1>"
  
  @app.route('/api/status')
  def status():
      return jsonify({"status": "ok"})
  
  if __name__ == "__main__":
      app.run(host="0.0.0.0", port=8080)
  

• Flask with SQLite Database:
  Prompt: “Extend the Flask app to connect to a SQLite database. Add a route `/users` that returns a JSON list of users from the database. If the database does not exist, create it and insert a sample user. Include error handling for database failures.”
• User Authentication (Flask):
  Prompt: “Implement a simple authentication system in Flask with `/register` and `/login` routes. Use werkzeug.security for password hashing and manage sessions with Flask. Ensure to handle errors like duplicate registrations or invalid credentials.”

Node.js & Express

• Basic Express Server:
  Prompt: “Write an Express application that listens on port 3000 and has the following routes: GET `/` returns an HTML welcome message; GET `/api/items` returns a JSON array of items; and POST `/api/items` adds a new item. Include Express JSON middleware and error handling middleware.”
• Express with MongoDB (CRUD):
  Prompt: “Using Express and Mongoose, create a REST API for a Todo app with endpoints to list, create, update, and delete todos. Each todo should have an id, title, and completed field. Handle errors for missing resources and validation.”
• JWT-based Authentication (Express):
  Prompt: “Implement JWT authentication in an Express app. Create routes `/auth/login` (to verify credentials and return a JWT) and `/auth/profile` (protected by a middleware that checks the token). Use the jsonwebtoken library and include error handling for invalid credentials or tokens.”

Debugging and Optimization Prompts

Troubleshooting & Error Fixes

• Bug Fix in JavaScript Factorial Function:
  Prompt: “The following JavaScript function should return the factorial of a number but fails for 0. Identify and fix the bug, and explain your solution.”

  function factorial(n) {
    if (n === 0) return 1;
    return n * factorial(n - 1);
  }
  console.log(factorial(0)); // Expected output: 1
  

• Python Runtime Error Analysis:
  Prompt: “Explain why the following Python code throws a ValueError when converting 'abc' to float, and provide a fix.”

  data = ["10", "20", "abc", "30"]
  numbers = [float(x) for x in data]
  print(sum(numbers))
  

• SQL Query Optimization:
  Prompt: “The query SELECT * FROM Orders WHERE customer_id = 12345 is slow on a table with millions of rows. Suggest at least two optimizations (e.g., using indexes or limiting columns) to improve performance.”

Guidelines on Iterating Prompts for Better Results

1. Start Simple, Then Add Detail: Begin with a basic prompt and add specifics as needed.
2. Use the Output as Feedback: Analyze the AI’s response and refine your prompt with additional details.
3. Incorporate Self-Correction: Ask the model to review its own output and improve it if needed.
4. Break Down Complex Tasks: Divide large tasks into smaller, manageable prompts.
5. Provide Examples or Counter-Examples: Show what you want (or don’t want) by including examples.
6. Experiment with Wording: Even slight changes in phrasing can yield better results.
7. Keep Track of Effective Prompts: Save prompts that work well for future use.
8. Know the Limits: Understand when further human review is needed.

Iterative refinement of your prompts will lead to higher quality AI-generated code. Use feedback to continuously improve your queries.

Conclusion

Using LLMs for web development can significantly accelerate your workflow—from generating boilerplate code to debugging complex issues. With clear, specific prompts and an iterative process, you can generate production-ready code for frontend, backend, and debugging tasks. Use this library as your reference to create robust and deployable websites, especially on platforms like Replit. Happy coding!