How to Use AI with zapgpt to Generate Git Commit Messages from a Git Diff

How to Use AI with zapgpt to Generate Git Commit Messages from a Git Diff

Writing useful Git commit messages can be surprisingly time-consuming, especially when a change touches multiple files. With zapgpt, you can export your repository’s diff and provide it to an AI model to generate a concise, meaningful commit message.

This workflow is simple:

1. Generate a Git diff.
2. Save the diff to a file.
3. Pass the file to zapgpt.
4. Ask the selected AI model to write a commit message.

Generate a Git Diff

From the root of your Git repository, run:

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git diff > git-diff.txt

This compares your working tree with the index and saves the output to git-diff.txt.

To include staged changes instead, use:

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git diff --cached > git-diff.txt

To include both staged and unstaged changes, generate the diff against HEAD:

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git diff HEAD > git-diff.txt

The resulting file contains the exact code changes that you can provide to the AI model.

Generate a Commit Message with zapgpt

Pass the diff file to zapgpt with the model and provider you want to use:

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zapgpt -m <model> -p <provider> -f git-diff.txt \
  "Write a concise Git commit message for this diff."

Replace the placeholders with your preferred model and provider. For example:

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zapgpt -m gpt-4o -p openai -f git-diff.txt \
  "Write a concise Git commit message for this diff."

The -f option supplies the contents of git-diff.txt to the prompt. The model can then analyze the changed files and produce a message based on the actual implementation.

Use a More Precise Prompt

The prompt in the command should request a commit message rather than another diff. A stronger prompt can enforce a consistent format:

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zapgpt -m <model> -p <provider> -f git-diff.txt \
  "Generate one concise Git commit message from this diff. Use Conventional Commits format. Return only the commit message."

A generated result might look like:

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feat(auth): add refresh token rotation

You can also request additional context when needed:

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zapgpt -m <model> -p <provider> -f git-diff.txt \
  "Analyze this Git diff and return:
1. One Conventional Commits message
2. A short explanation of the change
3. Any potential breaking changes"

For automation, ask the model to return only the message. This makes the output easier to copy directly into Git.

Generate a Commit Message for Staged Changes

A common workflow is to stage changes first, inspect them, and then ask the AI to write the commit message:

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git add .
git diff --cached > git-diff.txt

zapgpt -m <model> -p <provider> -f git-diff.txt \
  "Write one concise Conventional Commit message for these staged changes. Return only the message."

After reviewing the generated message, use it with Git:

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git commit -m "feat(auth): add refresh token rotation"

Do not commit the AI-generated message blindly. Review the diff and confirm that the message accurately describes the changes.

Create a Reusable Shell Function

If you use this workflow frequently, create a shell function:

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ai_commit_message() {
  git diff --cached > /tmp/git-diff.txt

  zapgpt -m "${1:-gpt-4o}" \
    -p "${2:-openai}" \
    -f /tmp/git-diff.txt \
    "Write one concise Conventional Commit message for these staged changes. Return only the commit message."
}

Run it like this:

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ai_commit_message gpt-4o openai

If your shell supports command substitution, you can use the generated output directly:

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git commit -m "$(zapgpt -m gpt-4o -p openai -f /tmp/git-diff.txt \
  'Write one concise Conventional Commit message for these staged changes. Return only the commit message.')"

Review the output before committing, especially when the diff contains complex or security-sensitive changes.

Protect Sensitive Repository Data

A Git diff can contain more than source code. It may include:

• API keys accidentally added to a file
• Internal URLs and hostnames
• Credentials or tokens
• Customer information
• Proprietary implementation details
• Comments containing sensitive operational data

Before sending a diff to an external AI provider, inspect it:

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less git-diff.txt

You can also search for common secret patterns:

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grep -Ein "api[_-]?key|secret|token|password|private[_-]?key" git-diff.txt

Remove sensitive data from the diff or use an approved self-hosted or enterprise AI provider when repository confidentiality matters. Ideally ensure that you do not commit that information to repo as well :).

Recommended End-to-End Workflow

Use this compact workflow for staged changes:

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git add .
git diff --cached > git-diff.txt

zapgpt -m <model> -p <provider> -f git-diff.txt \
  "Generate one concise Conventional Commit message for this diff. \
Return only the commit message."

rm git-diff.txt

Conclusion

Using zapgpt with a Git diff provides a fast way to generate consistent commit messages without manually summarizing every changed file. The basic workflow is:

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git diff --cached > git-diff.txt
zapgpt -m <model> -p <provider> -f git-diff.txt \
  "Write one concise Conventional Commit message for this diff."

For the best results, generate the diff from staged changes, use a precise prompt, review the model’s output, and check the diff for secrets before sending it to an AI provider.