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 explanationFollow Conventional Commits
— feat
, fix
, chore
, etc.max 72 chars
— keeps it readable in git logThe 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.
git add .
python /path/to/git_commit.py
Or wire it into a git alias:
git config --global alias.ai '!python /path/to/git_commit.py'
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.