How to beginner · 3 min read

How to use Claude API for code review

Q: How to use Claude API for code review

Use the anthropic Python SDK with your ANTHROPIC_API_KEY to call client.messages.create on a claude-3-5-sonnet-20241022 model, sending your code as user input and prompting Claude to review it. Parse the response from response.content[0].text for the review output.

Quick answer

Use the anthropic Python SDK with your ANTHROPIC_API_KEY to call client.messages.create on a claude-3-5-sonnet-20241022 model, sending your code as user input and prompting Claude to review it. Parse the response from response.content[0].text for the review output.

PREREQUISITES

Python 3.8+
Anthropic API key (free tier available)
pip install anthropic>=0.20

Setup

Install the official anthropic Python SDK and set your API key as an environment variable.

Install SDK: pip install anthropic
Set environment variable: export ANTHROPIC_API_KEY='your_api_key' (Linux/macOS) or set ANTHROPIC_API_KEY=your_api_key (Windows)

bash

pip install anthropic

Step by step

Use the anthropic.Anthropic client to send your code snippet with a prompt asking Claude to perform a code review. The example below shows a synchronous call with a Python function for review.

python

import os
import anthropic

client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])

code_to_review = '''
def add_numbers(a, b):
    return a + b
'''

prompt = f"""Please review the following Python code for correctness, style, and potential improvements:\n\n{code_to_review}"""

response = client.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=512,
    system="You are a helpful assistant specialized in code review.",
    messages=[{"role": "user", "content": prompt}]
)

print("Code review output:\n", response.content[0].text)

output

Code review output:
The function `add_numbers` correctly adds two numbers and returns the result. It is simple and clear. For style, consider adding type hints:

```python
def add_numbers(a: int, b: int) -> int:
    return a + b
```

Also, adding a docstring would improve code documentation.

Common variations

You can customize the code review by:

Using different Claude models like claude-sonnet-4-5 for faster or more detailed reviews.
Adjusting max_tokens for longer or shorter responses.
Implementing async calls with asyncio and client.messages.acreate for non-blocking code review.

python

import asyncio
import os
import anthropic

async def async_code_review():
    client = anthropic.Anthropic(api_key=os.environ["ANTHROPIC_API_KEY"])
    code = '''
    def multiply(x, y):
        return x * y
    '''
    prompt = f"Review this code:\n\n{code}"
    response = await client.messages.acreate(
        model="claude-3-5-sonnet-20241022",
        max_tokens=512,
        system="You are a helpful assistant specialized in code review.",
        messages=[{"role": "user", "content": prompt}]
    )
    print("Async code review output:\n", response.content[0].text)

asyncio.run(async_code_review())

output

Async code review output:
The function `multiply` correctly multiplies two numbers. It is concise and clear. Consider adding type hints and a docstring for better clarity.

Troubleshooting

If you get authentication errors, verify your ANTHROPIC_API_KEY environment variable is set correctly.
If responses are cut off, increase max_tokens.
For unexpected output, ensure your prompt clearly asks for a code review and includes the code snippet.

✅

Key Takeaways

Use the official anthropic SDK with claude-3-5-sonnet-20241022 for code review tasks.
Send your code as user input with a clear prompt requesting a review for best results.
Adjust max_tokens and model choice to balance detail and speed.
Async calls are supported via client.messages.acreate for scalable workflows.
Always set your API key securely in environment variables to avoid authentication issues.

Verified 2026-04 · claude-3-5-sonnet-20241022, claude-sonnet-4-5

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