How to refactor code with Gemini CLI — what are the best prompts?

How to Refactor Code with Gemini CLI

Gemini CLI is a powerful tool for code refactoring because it has direct access to your project files and understands your codebase context through

GEMINI.md

Setup for Refactoring

First, create a good

GEMINI.md

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# GEMINI.md

## Project
FastAPI backend, Python 3.11, PostgreSQL, SQLAlchemy 2.0

## Coding Standards
- Type hints required on all functions
- Docstrings for public functions
- Max function length: 30 lines
- Use async/await for all I/O
- Follow PEP 8

Best Refactoring Prompts

1. Refactor a specific file:

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gemini "Refactor src/auth.py to:
- Add type hints to all functions
- Extract the JWT logic into a separate JWTService class
- Add docstrings to all public methods
- Keep the same external interface so no callers break"

2. Extract a function:

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gemini "In src/api/users.py, the create_user endpoint is 80 lines long.
Extract the validation logic (lines 15-40) into a separate validate_user_input()
function. Keep the function in the same file."

3. Apply a pattern:

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gemini "Refactor all database queries in src/repositories/ to use the
Repository pattern. Create a BaseRepository class with common CRUD operations,
then have each repository inherit from it. Show me the plan first."

4. Performance refactoring:

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gemini "The process_orders() function in src/orders.py makes N+1 database queries.
Refactor it to use a single bulk query with joinedload. Preserve all existing behavior."

5. Large-scale refactoring with planning:

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gemini "I want to add async/await to the entire src/services/ directory.
First, show me all functions that need to change and any risks.
Then make the changes one file at a time, starting with the simplest."

Refactoring Workflow

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# Step 1: Give context and get a plan
gemini "Review src/payment.py and suggest refactoring improvements. List them by priority."

# Step 2: Approve and execute the most important one
gemini "Implement refactoring #1 from your previous suggestions: extract PaymentProcessor class"

# Step 3: Verify
gemini "Run the tests for src/payment.py and check if they all pass"

# Step 4: Address any test failures
gemini "Test test_payment_timeout is failing. What changed and how to fix it?"

Effective Prompt Patterns

Common Refactoring Tasks

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# Add type hints everywhere
gemini "Add complete type hints to all functions in src/. Start with the files
that have no type hints at all."

# Fix code duplication
gemini "There's duplicated validation logic in users.py and orders.py.
Extract it to a shared utils/validators.py module."

# Modernize Python syntax
gemini "Update all f-string formatting and replace old % formatting
with f-strings throughout the src/ directory."

# Improve error handling
gemini "Review src/api/ and add proper error handling with specific exception
types instead of bare except clauses."

Tips for Better Refactoring Results

• Include relevant files in context:
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  gemini @src/auth.py "Refactor the JWT handling"

• Specify constraints: "Do not change the public API"
• Ask for impact assessment first: "What would break if I extract this?"
• Review changes before accepting
• Commit before refactoring so you can compare/rollback