Understanding Existing Code

# Get a high-level overview:
> Read the directory structure and main files.
  Describe this project in 3-5 sentences: what does it do,
  what technology stack does it use, and how is it organized?

# Understand the entry points:
> Where does a web request enter this application?
  Trace the path from the URL to the first PHP/Python file that handles it.

# Find the database:
> What database tables exist in this project?
  Find schema files, migration files, or CREATE TABLE statements.
  List each table and its main purpose.

# Map the major components:
> What are the main "areas" of this codebase?
  For example: auth, products, orders, admin panel.
  Which files/directories handle each area?

> Explain this code line by line in simple terms:
  [paste 10-30 lines of code]

> What does this function do and what does it return?
  [paste function]

> I see this pattern used everywhere in this codebase:
  [paste code pattern]
  What is this pattern called and why is it used here?

> This code uses the Repository pattern. Can you explain it in
  simple terms and show me which classes are repositories in this project?

> Read the UserModel class. Describe:
  1. What data it manages
  2. What each public method does (one sentence each)
  3. Any non-obvious design choices
  4. What other classes depend on it

> Read the AuthController. Walk me through the login flow step by step,
  from when the form is submitted to when the user reaches the dashboard.

# Trace a user action:
> Trace exactly what happens when a user clicks "Place Order" on the checkout page.
  Follow the code path: which files are executed in which order,
  what data is passed between them, and what is ultimately saved to the database.

# Trace data through layers:
> How does a product get from the database to the HTML page?
  Trace from the SQL query through any transformations to the final output.

# Find where something is set/read:
> In which files is the $_SESSION['user_id'] variable set and read?
  Find every place it is used and what it is used for.

# Find dependencies:
> Which parts of the code depend on the PaymentGateway class?
  If I change its interface, which files would break?

# Add PHPDoc to all methods:
> Add PHPDoc comments to every public method in this class.
  Include @param, @return, and a one-sentence description.
  [paste class]

# Write a README section:
> Read the /app/services/ directory. Write a README.md section
  that explains what each service class does and when to use it.

# Document the database schema:
> Read all the CREATE TABLE statements in /database/schema.sql.
  Write a DATABASE.md file that describes each table's purpose,
  important columns, and relationships to other tables.

# Document a complex algorithm:
> This function implements a complex calculation. Add inline comments
  that explain the purpose of each step, not just what the code does.
  [paste function]

# Step 1: Get oriented (run this first in a new project):
> I am new to this codebase. Read the project files and answer:
  1. What does this application do?
  2. What is the tech stack?
  3. How do I run it locally?
  4. Where is the main configuration?
  5. What are the 5 most important files to understand first?

# Step 2: Understand the architecture:
> Describe the architecture of this application.
  How is the code organized? Does it use MVC, service layer,
  repository pattern, or something else?

# Step 3: Find the important stuff:
> Where is:
  - User authentication handled?
  - The database connection configured?
  - The main routing logic?
  - Email sending?
  - Error logging?

# Step 4: Understand the data model:
> Read the database schema and draw (in text) the entity relationships.
  Which tables are central and which are peripheral?

> I want to change the getUserById() method in UserModel.
  Which other files call this method?
  What would break if I change its return type from array to object?

> I want to rename the 'email' column in the users table to 'email_address'.
  Find every place in the codebase that references 'email' in a database query
  or result. List the files and lines I would need to update.

> I want to add a required 'tenant_id' parameter to the UserModel constructor.
  How many places create a new UserModel? List them all.

> Before I modify the checkout flow, which automated tests cover it?
  Run the test suite and show me which tests would be affected.