Commit Message Git Hook

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.
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):

#!/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

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:

{ 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:

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:

... | 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

Recipes

Commit Message Git Hook

How It Works

Prerequisites

Step 1: Install the hook

Step 2: Use it

Step 3: Test it without committing

Variations

Troubleshooting

Where to Go Next

Private Code Review Pipeline

Scripting and Automation

​How It Works

​Prerequisites

​Step 1: Install the hook

​Step 2: Use it

​Step 3: Test it without committing

​Variations

​Troubleshooting

​Where to Go Next

Private Code Review Pipeline

Scripting and Automation

How It Works

Prerequisites

Step 1: Install the hook

Step 2: Use it

Step 3: Test it without committing

Variations

Troubleshooting

Where to Go Next