marcus · iamlasse · Jun 28, 2026 · Jun 29, 2026
diff --git a/AGENTS.md b/AGENTS.md
@@ -43,3 +43,7 @@ go test ./...
 - **Style**: Standard Go (gofmt, govet). No magic, explicit is better.
 - **Errors**: Wrap with context, don't swallow.
 - **Tests**: Table-driven, in `_test.go` files alongside code.
+- **Commits**: Conventional Commits (`<type>(<scope>): <subject>`). Allowed
+  types: `feat fix docs style refactor test chore perf build ci`. Lowercase,
+  imperative subject, max 72 chars. Install the commit-msg hook with
+  `make install-hooks`; see `docs/commit-messages.md` for details.
diff --git a/Makefile b/Makefile
@@ -75,10 +75,13 @@ help:
 	@echo "  check         - Run tests and lint"
 	@echo "  install       - Build and install to Go bin directory"
 	@echo "  calibrate-providers - Compare local Claude/Codex session usage for calibration"
-	@echo "  install-hooks  - Install git pre-commit hook"
+	@echo "  install-hooks  - Install git hooks (pre-commit + commit-msg)"
 	@echo "  help          - Show this help"
 
-# Install git pre-commit hook
+# Install git hooks (pre-commit quality gate + commit-msg normalizer)
 install-hooks:
 	@ln -sf ../../scripts/pre-commit.sh .git/hooks/pre-commit
+	@ln -sf ../../scripts/commit-msg.sh .git/hooks/commit-msg
+	@chmod +x scripts/commit-msg.sh
 	@echo "✓ pre-commit hook installed (.git/hooks/pre-commit → scripts/pre-commit.sh)"
+	@echo "✓ commit-msg hook installed (.git/hooks/commit-msg → scripts/commit-msg.sh)"
diff --git a/README.md b/README.md
@@ -258,18 +258,46 @@ Each task has a default cooldown interval to prevent the same task from running
 
 ## Development
 
-### Pre-commit hooks
+### Commit messages
 
-Install the git pre-commit hook to catch formatting and vet issues before pushing:
+Nightshift uses [Conventional Commits](https://www.conventionalcommits.org/)
+for every commit message, so history stays readable and tooling can derive
+changelogs automatically. The format is:
+
+```
+<type>(<scope>): <subject>
+
+<body>
+```
+
+- **type** — one of `feat`, `fix`, `docs`, `style`, `refactor`, `test`,
+  `chore`, `perf`, `build`, `ci`.
+- **scope** — optional, e.g. `fix(api): ...`.
+- **subject** — lowercase, imperative mood, no trailing period, max 72 chars.
+- **body** — optional, wrapped at 72 columns, separated from the subject by a
+  blank line.
+
+See [`docs/commit-messages.md`](docs/commit-messages.md) for full details,
+including the `nightshift commit normalize` command.
+
+### Git hooks
+
+Install the git hooks to catch formatting/vet issues and to enforce the
+Conventional Commits format before pushing:
 
 ```bash
 make install-hooks
 ```
 
-This symlinks `scripts/pre-commit.sh` into `.git/hooks/pre-commit`. The hook runs:
-- **gofmt** — flags any staged `.go` files that need formatting
-- **go vet** — catches common correctness issues
-- **go build** — ensures the project compiles
+`make install-hooks` symlinks two scripts into `.git/hooks/`:
+
+- **pre-commit** (`scripts/pre-commit.sh`) runs:
+  - **gofmt** — flags any staged `.go` files that need formatting
+  - **go vet** — catches common correctness issues
+  - **go build** — ensures the project compiles
+- **commit-msg** (`scripts/commit-msg.sh`) normalizes the commit message into
+  canonical Conventional Commits form and rejects messages that cannot be
+  normalized (missing/unknown type, capitalized or overlong subject).
 
 To bypass in a pinch: `git commit --no-verify`
 

diff --git a/cmd/nightshift/commands/commit.go b/cmd/nightshift/commands/commit.go
@@ -0,0 +1,88 @@
+package commands
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/marcus/nightshift/internal/commits"
+	"github.com/spf13/cobra"
+)
+
+var commitCmd = &cobra.Command{
+	Use:   "commit",
+	Short: "Conventional Commits helpers",
+	Long: `Tools for working with Conventional Commits messages.
+
+Use "commit normalize" to validate and reformat a commit message so it
+follows the project's rules (type prefix, lowercase type, subject length,
+and wrapped body).`,
+}
+
+var commitNormalizeCmd = &cobra.Command{
+	Use:   "normalize [MESSAGE]",
+	Short: "Normalize a commit message to Conventional Commits format",
+	Long: `Validate and rewrite a commit message into canonical Conventional
+Commits form.
+
+The message is read from a positional argument, from a file passed via
+--file (typically .git/COMMIT_EDITMSG by a commit-msg hook), or from stdin
+when no argument and no --file are given.
+
+  nightshift commit normalize "feat: add login"
+  nightshift commit normalize --file .git/COMMIT_EDITMSG
+  git log -1 --pretty=%B | nightshift commit normalize
+
+Use --check to only validate without rewriting; the exit code is non-zero
+when the message does not conform.`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		check, _ := cmd.Flags().GetBool("check")
+		file, _ := cmd.Flags().GetString("file")
+
+		raw, err := readCommitMessage(args, file)
+		if err != nil {
+			return err
+		}
+
+		normalized, err := commits.Normalize(raw)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "error: %v\n", err)
+			return err
+		}
+
+		if check {
+			fmt.Fprintln(os.Stdout, normalized)
+			return nil
+		}
+		fmt.Fprintln(os.Stdout, normalized)
+		return nil
+	},
+}
+
+func init() {
+	commitNormalizeCmd.Flags().BoolP("check", "c", false, "Only validate; do not rewrite")
+	commitNormalizeCmd.Flags().StringP("file", "f", "", "Read the message from this file (use by the commit-msg hook)")
+	commitCmd.AddCommand(commitNormalizeCmd)
+	rootCmd.AddCommand(commitCmd)
+}
+
+// readCommitMessage resolves the message source in order: positional arg,
+// --file, then stdin.
+func readCommitMessage(args []string, file string) (string, error) {
+	if len(args) == 1 {
+		return args[0], nil
+	}
+	if file != "" {
+		b, err := os.ReadFile(file)
+		if err != nil {
+			return "", fmt.Errorf("read %s: %w", file, err)
+		}
+		return string(b), nil
+	}
+	b, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		return "", fmt.Errorf("read stdin: %w", err)
+	}
+	return string(b), nil
+}
diff --git a/docs/commit-messages.md b/docs/commit-messages.md
@@ -0,0 +1,47 @@
+# Commit Messages
+
+Nightshift uses [Conventional Commits](https://www.conventionalcommits.org/)
+for all commit messages. This keeps the history readable and lets tooling
+derive changelogs automatically.
+
+## Format
+
+```
+<type>(<scope>): <subject>
+
+<body>
+```
+
+- **type** — one of `feat`, `fix`, `docs`, `style`, `refactor`, `test`,
+  `chore`, `perf`, `build`, `ci`.
+- **scope** — optional, e.g. `fix(api): ...`.
+- **subject** — lowercase, imperative mood, no trailing period, max 72 chars.
+- **body** — optional, wrapped at 72 columns, separated from the subject by a
+  blank line.
+
+## The `commit normalize` command
+
+Validate and reformat a message:
+
+```sh
+nightshift commit normalize "feat: add login screen"
+nightshift commit normalize --file .git/COMMIT_EDITMSG
+git log -1 --pretty=%B | nightshift commit normalize
+```
+
+Add `--check` to validate only. The command exits non-zero when a message
+cannot be normalized (missing/unknown type, capitalized or overlong subject).
+
+## commit-msg hook
+
+To enforce the rules locally, install the hook:
+
+```sh
+make install-hooks
+# or manually:
+ln -sf ../../scripts/commit-msg.sh .git/hooks/commit-msg
+```
+
+The hook normalizes your message file in place before the commit is created and
+rejects messages that cannot be fixed automatically. Bypass it with
+`git commit --no-verify`.