I Fixed the "AI Commit Messages" Problem in 20 Lines of Python

You've probably seen that trending post — "I Asked AI to Write My Commit Messages and It Was Embarrassing." Same. But instead of accepting embarrassing output, I fixed it. Here's the thing: the problem isn't AI writing commit messages. The problem is how you ask it. One clear system prompt + the actual diff = surprisingly good results. No new packages. No API key. If you have Claude Code, you're already set. #!/usr/bin/env python3 import subprocess SYSTEM = ( "You are a git commit message generator. " "Output ONLY the commit message — no explanation, no markdown, no quotes. " "Follow Conventional Commits: type(scope): subject. " "Types: feat, fix, docs, style, refactor, test, chore. " "Subject: imperative, lowercase, max 72 chars." ) diff = subprocess.check_output(["git", "diff", "--staged"], text=True) if not diff.strip(): print("Nothing staged. Run `git add` first.") raise SystemExit(1) msg = subprocess.check_output( ["claude", "-p", SYSTEM + "\n\n" + diff], text=True, ).strip() print(msg) That's it. 20 lines. Uses the claude CLI under the hood — no API key, no config, just your existing Claude Code OAuth session. The system prompt does the heavy lifting. Three constraints: Output ONLY the commit message — no preamble, no explanation Follow Conventional Commits — feat, fix, chore, etc. max 72 chars — keeps it readable in git log The diff is the context. You're not asking "write a commit message". You're asking "given these exact changes, what happened?" That's a much more answerable question. # No setup needed if you have Claude Code. Just: git add . python /path/to/git_commit.py # → feat(server): add AI commit message generator via Claude CLI Or wire it into a git alias: git config --global alias.ai '!python /path/to/git_commit.py' # git ai Before: update stuff fix bug WIP added the thing After: feat(api): add generate_commit_message tool to MCP server fix(auth): handle expired token on refresh refactor(db): extract query builder into separate module I also wrapped it as an MCP tool so Claude Code can call it directly from any conversation: @mcp.tool() def generate_commit_message(diff: str) -> str: """Generate a Conventional Commits message from a git diff string.""" full = SYSTEM + "\n\n" + diff return subprocess.check_output(["claude", "-p", full], text=True).strip() Full project: github.com/enjoy-kumawat/my-git-manager 20 lines. No new dependencies. No API key. Conventional Commits every time. The embarrassing part was waiting this long to build it.