cmtr

cmtr writes your git commit messages for you. It prefers Codex CLI (using your ChatGPT account) and also supports the OpenAI API. Both backends default to gpt-6-luna. It uses the staged diff and recent commit history to match the repository's style.

Quick start (recommended)

1. Install uv (if needed), then run:
   • uvx cmtr@latest
2. Optional: add a shell alias:
   • alias cmtr="uvx cmtr@latest"
3. Authenticate (preferred: Codex):
   • Codex CLI (preferred): run npx @openai/codex@latest and sign in (uses your ChatGPT account)
   • API key (alternative): export OPENAI_API_KEY=...
4. Stage changes and run:
   • git add -A
   • cmtr

Codex mode is preferred because it uses your ChatGPT account usage (not separate API billing) and requires no API key. If Codex isn't on your PATH, cmtr will run it via npx @openai/codex@latest as long as you're signed in. If Codex is unavailable and OPENAI_API_KEY is set, cmtr falls back to the OpenAI API. OpenAI API requests are sent with store = false.

Or install the git hook:

• cmtr --hook
  • Installs a prepare-commit-msg hook that automatically generates a commit message right before the commit editor opens. If there is already a message or you're in a rebase/fixup/squash flow, it skips.
  • If the repo sets core.hooksPath in its local git config, cmtr installs the hook in that directory. If only a global core.hooksPath is set, re-run with --global or set a local override with git config --local core.hooksPath .git/hooks.
  • If a .pre-commit-config.yaml/.yml is present, cmtr will prompt to install a pre-commit prepare-commit-msg hook instead (adds an entry that runs uvx cmtr@latest prepare-commit-msg). You may need to run pre-commit install --hook-type prepare-commit-msg after accepting.

Usage

• cmtr
  • Behaves like git commit -v, but injects a generated commit message.
• cmtr --dry-run
  • Print the generated message without committing.
• cmtr --print-prompt
  • Print the prompts used to generate the message.
• cmtr --no-edit
  • Skip opening the editor after generating the message.
• cmtr --model gpt-6-luna
  • Override the selected backend's model for this run.
• cmtr --codex-model gpt-6-luna
  • Override only the Codex CLI model for this run.
• cmtr --organization org_... --project proj_...
  • Override the OpenAI organization/project for this run.
• cmtr --hook
  • Install the prepare-commit-msg hook to auto-generate messages on every commit.
• cmtr --global --hook
  • Install the hook in the globally configured hooks path.
• cmtr --uninstall-hook
  • Remove the hook.

Extra git commit flags can be passed directly (for example, --no-verify). cmtr rejects message-supplying, message-shaping, and content-changing flags such as -a, -i, -o, -m, -F, -t, -C, -c, --amend, --allow-empty, --cleanup, --fixup, --squash, --patch, --interactive, --dry-run, -e, --edit, --no-edit, --include, --only, --pathspec-from-file, and their attached/long-form equivalents because cmtr supplies the message, controls editor behavior, and analyzes the staged diff before running git commit. Safe metadata/trailer options such as --author, --date, --signoff, --gpg-sign, and --trailer are passed through. Pathspecs passed after -- are supported and limit the prompt context to those staged paths. They are interpreted relative to the current directory, like git commit. If those paths also have unstaged edits, cmtr stops instead of generating a message from stale staged context. AI backends are asked to return structured JSON with a single message string. cmtr validates that string before use; obvious prompt leaks, diff echoes, conflict markers, placeholders, malformed body spacing, and comment-only output are rejected instead of being rewritten with heuristic cleanup.

How it builds context

• Uses staged files (git diff --cached) for the actual changes.
• Finds shared paths and samples recent git log messages on those paths to learn the repo's style.
• For unrelated staged files, samples up to max_log_paths high-signal paths instead of relying on only one fallback path.
• Requests structured output from the model so the generated commit message is returned as data, not prose wrapped around a suggestion.
• Codex mode runs from a scratch directory and receives only the generated prompt context, not live access to the target checkout.

Configuration

Configuration is loaded in this order (later overrides earlier):

1. XDG config file (~/.config/cmtr/config.toml or $XDG_CONFIG_HOME/cmtr/config.toml)
2. cmtr.toml in the repo root (optional repo-specific overrides)
3. Environment variables
4. CLI flags

Manage global config with:

• cmtr config path
• cmtr config list
• cmtr config get model
• cmtr config set model gpt-6-luna
• cmtr config unset model

Example config file:

model = "gpt-6-luna"
codex_model = "gpt-6-luna"
max_diff_bytes = 12000
max_patch_lines = 400
max_log_entries = 20
max_log_paths = 4
max_log_body_lines = 6
timeout_seconds = 60
reasoning_effort = ""
text_verbosity = "low"
prefer_codex = true
base_url = "https://api.openai.com/v1"
organization = "org_..."
project = "proj_..."

Unknown config keys and invalid numeric ranges fail fast so typoed settings do not silently fall back to defaults. model/CMTR_MODEL configures OpenAI API mode. codex_model/CMTR_CODEX_MODEL configures Codex mode. For one-off CLI runs, --model overrides whichever backend is selected, while --codex-model overrides only Codex mode. Set reasoning_effort or text_verbosity to a blank string to avoid sending that optional Responses API parameter for models or compatible providers that do not support it.

Codex is preferred by default. timeout_seconds applies to both Codex CLI execution and OpenAI API requests. Set prefer_codex = false to use the OpenAI API first whenever OPENAI_API_KEY is set, while still allowing Codex when no API key is available. Use cmtr auth status to see which mode will be selected and why.

Environment variables:

• OPENAI_API_KEY
• OPENAI_BASE_URL
• OPENAI_ORG_ID (also supports OPENAI_ORG and OPENAI_ORGANIZATION)
• OPENAI_PROJECT_ID
• CMTR_MODEL
• CMTR_CODEX_MODEL
• CMTR_MAX_DIFF_BYTES
• CMTR_MAX_PATCH_LINES
• CMTR_MAX_LOG_ENTRIES
• CMTR_MAX_LOG_PATHS
• CMTR_MAX_LOG_BODY_LINES
• CMTR_TIMEOUT_SECONDS
• CMTR_REASONING_EFFORT
• CMTR_TEXT_VERBOSITY
• CMTR_PREFER_CODEX

Development

Local development:

• mise install
• mise run install
• mise run run

Linting and type checking:

• mise run lint
• uv run ruff check .
• mise run format-check
• uv run ruff format --check .
• mise run typecheck
• uv run ty check

Testing and packaging:

• mise run format
• uv run ruff format .
• mise run test
• uv run pytest
• mise run build
• uv build

If you are installing manually, run uv sync --group dev first to install the dev tools.

Troubleshooting

• No staged changes: run git add before cmtr.
• Missing API key: set OPENAI_API_KEY or install/login to Codex CLI.
• Unsure which auth mode is active: run cmtr auth status.
• Hook failures: a # cmtr failed: ... comment is appended to the commit message template.