> ## Documentation Index > Fetch the complete documentation index at: https://docs.trynito.ai/llms.txt > Use this file to discover all available pages before exploring further. # Commit Message Git Hook > Prefill your commit messages from the staged diff with a Nito git hook, using nito ask over stdin, that fails open so it never blocks a commit. **Goal.** Stop writing commit messages by hand. This recipe installs a `prepare-commit-msg` git hook that sends your staged diff to Nito and prefills the commit-message editor with a suggestion you can accept or edit. It **fails open**: if Nito is unavailable, the commit proceeds untouched, so the hook can never block your work. **When to reach for it.** Any repo where you want consistent one-line commit messages without the friction. It runs locally on every `git commit`. ## How It Works Git runs a `prepare-commit-msg` hook after you type `git commit` but before the editor opens, and passes it the path to the commit-message file (and, for some commit types, a source). The hook reads your staged diff, pipes it to `nito ask --stdin --quiet`, and writes the one-line suggestion into that file, where it appears prefilled in your editor. Two design choices keep it safe: * **It only prefills a plain `git commit`.** For `git commit -m`, merges, squashes, and amends, the message already exists, and git sets a commit source in those cases. The hook checks for that source and exits without touching anything. * **It fails open.** The suggestion is written only if `nito ask` succeeded. If Nito is down or you are offline, the commit proceeds with the normal empty template. A helper that blocks commits would be worse than no helper. ## Prerequisites * **Nito installed and signed in.** See [Nito CLI](/cli/reference). * A git repository. ## Step 1: Install the hook Save this as `.git/hooks/prepare-commit-msg` in your repo and make it executable (`chmod +x .git/hooks/prepare-commit-msg`): ```bash theme={"theme":{"light":"github-light","dark":"github-dark"},"languages":{"custom":["typescript","python","curl"]}} #!/usr/bin/env bash set -euo pipefail MSG_FILE="$1" COMMIT_SOURCE="${2:-}" # Only prefill a plain `git commit`. Skip -m, merges, squashes, and amends, # which already carry a message ($COMMIT_SOURCE is set in those cases). [ -n "$COMMIT_SOURCE" ] && exit 0 diff=$(git diff --staged) [ -z "$diff" ] && exit 0 # Ask Nito for a one-line message. Fail open: on any error, leave the commit # untouched so the hook never blocks you. if suggestion=$( { echo "Write a one-line Conventional Commits message (type: summary) for this" echo "staged diff. Imperative mood, under 72 characters, no body, no backticks:" echo echo "$diff" } | nito ask --stdin --quiet --web-search off 2>/dev/null ); then # Prepend the suggestion above the existing template in the message file printf '%s\n\n%s\n' "$suggestion" "$(cat "$MSG_FILE")" > "$MSG_FILE" fi ``` The parts that matter: * **`COMMIT_SOURCE` guard** skips the hook whenever a message already exists, so it only prefills a plain `git commit`. * **`--stdin`** takes the whole prompt from the pipe, so the instruction and the diff go in together. * **`--quiet`** returns only the message text, nothing to strip. * **`if suggestion=$(…); then`** writes the file only on success, which is what makes the hook fail open. ## Step 2: Use it ```bash theme={"theme":{"light":"github-light","dark":"github-dark"},"languages":{"custom":["typescript","python","curl"]}} git add -p git commit # editor opens with a suggested message prefilled ``` Accept the suggestion, edit it, or clear it and write your own. Nothing is committed until you save and close the editor as usual. ## Step 3: Test it without committing To see what the hook would produce without making a commit, run its core against your staged changes directly: ```bash theme={"theme":{"light":"github-light","dark":"github-dark"},"languages":{"custom":["typescript","python","curl"]}} { echo "Write a one-line Conventional Commits message for this diff, no backticks:"; git diff --staged; } \ | nito ask --stdin --quiet --web-search off ``` Stage a small change first, then run it, and tune the instruction until the style is what you want. ## Variations **Team-shared hook.** `.git/hooks` is not committed, so it is per-clone. To share the hook across a team, keep it in the repo (for example `scripts/hooks/`) and point git at that directory once: ```bash theme={"theme":{"light":"github-light","dark":"github-dark"},"languages":{"custom":["typescript","python","curl"]}} git config core.hooksPath scripts/hooks ``` **Richer messages.** Ask for a subject line and a short body by changing the instruction, for example: "a Conventional Commits subject line, then a blank line, then two bullet points." **Pin a private model.** Keep diffs off any frontier provider by pinning a fast Private-tier model in the hook's `nito ask` line: ```bash theme={"theme":{"light":"github-light","dark":"github-dark"},"languages":{"custom":["typescript","python","curl"]}} ... | nito ask --stdin --quiet --web-search off --model z-ai/glm-5.2 2>/dev/null ``` ## Troubleshooting | What you see | Why | Fix | | :--------------------------------- | :------------------------------------------ | :------------------------------------------------------------------------- | | No suggestion appears | Nito was unavailable, or nothing was staged | The hook fails open by design; stage changes and check `nito agent status` | | The hook does not run | Not executable, or wrong path | `chmod +x .git/hooks/prepare-commit-msg`; confirm the exact filename | | It overwrites a `-m` message | The `COMMIT_SOURCE` guard was removed | Keep the `[ -n "$COMMIT_SOURCE" ] && exit 0` line | | Message has stray quotes or fences | The model added formatting | Add "no backticks, no quotes" to the instruction | ## Where to Go Next Review the same staged diff across models before you commit. Exit codes, stdin, and output modes for hooks and pipelines.