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

A developer created a 20-line Python script that generates high-quality git commit messages using Claude Code's CLI. The script combines a strict system prompt enforcing Conventional Commits format with the actual staged diff, eliminating the need for API keys or additional packages. The tool is available as a standalone script or an MCP tool for Claude Code.

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 https://claude.ai/code , you're already set. python /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: php @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 https://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.