auto-commit-msg (acm)

Generates a commit message from a git diff using AI.

Features

• Supports OpenAI-like providers, with Gemini as the default.
• Improve commit messages by switching to a model based on diff size.

Note

The commit messages for this project were generated using this tool.

Installation

Download the precompiled binary from the releases page that matches your current system. Unzip the file and place the binary in a location available on your PATH environment variable.

Instructions for non-Nix users

pre-commit

Add a .pre-commit-config.yaml file to your project's root directory with the following content:

- repo: local
  hooks:
    - id: auto-commit-msg
      name: auto-commit-msg
      entry: acm
      language: system
      stages: [prepare-commit-msg]

Instructions for Nix users

devenv

Add the auto-commit-msg input to the devenv.yaml file:

inputs:
  auto-commit-msg:
    url: github:sestrella/auto-commit-msg
    overlays: [default]
  nixpkgs:
    url: github:cachix/devenv-nixpkgs/rolling

Add the auto-commit-msg hook to the devenv.nix file as follows:

{ pkgs, lib, ... }:

{
  dotenv.enable = true;

  git-hooks.hooks.auto-commit-msg = {
    enable = true;
    entry = lib.getExe pkgs.auto-commit-msg;
    stages = [ "prepare-commit-msg" ];
  };

  cachix.pull = [ "sestrella" ];
}

Note: Enabling dotenv is optional if the OPENAI_API_KEY environment variable is available.

Configuration

auto-commit-msg can be configured via a .auto-commit-msg.toml file in the project's root directory or the user's home directory. The available configuration parameters are:

• trace: When true, appends auto-commit-msg execution traces to the commit message.

  • Default: false

  The following metrics are appended to the commit message when trace is enabled:

  • Version: The version of the auto-commit-msg command used.
  • Model: The model used to generate the commit message.
  • ResponseTime: The time it took to get a response from the AI model.
  • ExecutionTime: The total time it took for the auto-commit-msg command to execute.

• provider.base_url: The base URL of the OpenAI-like provider.

  • Default: https://generativelanguage.googleapis.com/v1beta/openai

• provider.api_key: The name of the environment variable that contains the API key.

  • Default: GEMINI_API_KEY

• diff.short_model: The model to use for diffs with fewer lines than diff.threshold.

  • Default: gemini-2.5-flash-lite

• diff.long_model: The model to use for diffs with more lines than diff.threshold.

  • Default: gemini-2.5-flash

• diff.threshold: The line count threshold to switch between diff.short_model and diff.long_model.

  • Default: 500

Here is an example .auto-commit-msg.toml file:

trace = true

[provider]
base_url = "https://api.openai.com/v1"
api_key = "OPENAI_API_KEY"

[diff]
short_model = "gpt-4.1-mini"
long_model = "o4-mini"
threshold = 250

Usage

After setting auto-commit-msg as a prepare-commit-msg hook, invoking git commit without a commit message generates a commit message. If a commit message is given, auto-commit-msg does not generate a commit message and instead uses the one provided by the user.

Benchmark

The following table compares the Go and Rust implementations; it was built using hyperfine.

Command	Mean [s]	Min [s]	Max [s]	Relative
./auto-commit-msg	1.101 ± 0.205	0.776	1.309	1.00
./rust/target/release/acm	1.244 ± 0.106	1.127	1.416	1.13 ± 0.23

License

MIT