Summarize Git Diffs with Claude AI

Use the Claude API to auto-generate pull request summaries from git diffs. Working Python code plus an instant no-code tool.

Claude's large context window and code understanding make it ideal for automated PR reviews and diff summaries. This guide shows the minimal Python implementation, plus links to a no-code tool for one-off reviews.

Quick implementation

import subprocess
import anthropic

def summarize_diff(base="HEAD~1", head="HEAD"):
    diff = subprocess.check_output(
        ["git", "diff", base, head], text=True
    )
    if not diff.strip():
        return "No changes detected."

    client = anthropic.Anthropic()
    message = client.messages.create(
        model="claude-sonnet-4-6",
        max_tokens=1024,
        messages=[{
            "role": "user",
            "content": f"""You are a senior code reviewer. Summarize this git diff:

{diff}

Output:
1. One-sentence overall summary
2. Changed files (bullet list, what changed in each)
3. Potential bugs or risks
4. Suggestions for improvement"""
        }]
    )
    return message.content[0].text

print(summarize_diff())

Summarize any branch diff

# Compare feature branch to main
diff = subprocess.check_output(
    ["git", "diff", "main...feature/my-branch"], text=True
)

# Or get staged changes only
diff = subprocess.check_output(
    ["git", "diff", "--cached"], text=True
)

# Or compare specific files
diff = subprocess.check_output(
    ["git", "diff", "HEAD~1", "HEAD", "--", "src/api.py"], text=True
)

Structured output for CI integration

import json

def structured_diff_review(diff_text):
    client = anthropic.Anthropic()
    message = client.messages.create(
        model="claude-sonnet-4-6",
        max_tokens=2048,
        messages=[{
            "role": "user",
            "content": f"""Review this git diff and respond ONLY with valid JSON:

{diff_text}

{{
  "summary": "one sentence overall summary",
  "files_changed": [{{"file": "path/to/file.py", "changes": "what changed"}}],
  "risks": ["list of potential bugs or security issues"],
  "suggestions": ["list of improvement suggestions"],
  "severity": "low|medium|high"
}}"""
        }]
    )
    return json.loads(message.content[0].text)

# Use in CI pipeline
review = structured_diff_review(diff)
if review["severity"] == "high":
    print("⚠️ High-risk changes detected — requires senior review")
    for risk in review["risks"]:
        print(f"  - {risk}")

Stream the review for large diffs

def stream_diff_summary(diff_text):
    client = anthropic.Anthropic()
    with client.messages.stream(
        model="claude-sonnet-4-6",
        max_tokens=2048,
        messages=[{"role": "user", "content": f"Review this diff:\n\n{diff_text}"}]
    ) as stream:
        for text in stream.text_stream:
            print(text, end="", flush=True)
    print()  # newline at end

# Good for very large PRs where you want to see output as it arrives
stream_diff_summary(diff)

No-code alternative

Don't want to write code? The AI Diff Summarizer lets you paste any git diff and get an instant Claude-powered code review. No API key needed — ideal for one-off reviews or sharing with teammates.

Cost estimate

Use the Claude API Cost Calculator to estimate costs for your specific diff sizes.

Frequently asked questions

Free tools

More examples