diff --git a/Makefile b/Makefile
index 088be01..152244e 100644
--- a/Makefile
+++ b/Makefile
@@ -75,10 +75,12 @@ 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"
 	@echo "  help          - Show this help"
 
-# Install git pre-commit hook
+# Install git hooks
 install-hooks:
 	@ln -sf ../../scripts/pre-commit.sh .git/hooks/pre-commit
+	@ln -sf ../../scripts/commit-msg.sh .git/hooks/commit-msg
 	@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
index 84f92cd..f9524a8 100644
--- a/README.md
+++ b/README.md
@@ -258,19 +258,38 @@ Each task has a default cooldown interval to prevent the same task from running
 
 ## Development
 
-### Pre-commit hooks
+### Git hooks
 
-Install the git pre-commit hook to catch formatting and vet issues before pushing:
+Install the git hooks to catch formatting, vet, build, and commit message issues before pushing:
 
 ```bash
 make install-hooks
 ```
 
-This symlinks `scripts/pre-commit.sh` into `.git/hooks/pre-commit`. The hook runs:
+This symlinks `scripts/pre-commit.sh` into `.git/hooks/pre-commit` and `scripts/commit-msg.sh` into `.git/hooks/commit-msg`.
+
+The pre-commit hook runs:
 - **gofmt** — flags any staged `.go` files that need formatting
 - **go vet** — catches common correctness issues
 - **go build** — ensures the project compiles
 
+The commit message hook accepts:
+
+```text
+type: summary
+type(scope): summary
+```
+
+Accepted types are `feat`, `fix`, `docs`, `test`, `refactor`, `chore`, `build`, `ci`, `perf`, `style`, and `revert`. The hook normalizes safe cases such as `FIX: thing`, `feat - thing`, and extra whitespace, while preserving the body and trailers. Merge, revert, `fixup!`, and `squash!` commits are allowed.
+
+Valid examples:
+
+```text
+feat: add project setup command
+fix(config): preserve default provider
+docs: document hook installation
+```
+
 To bypass in a pinch: `git commit --no-verify`
 
 ## Uninstalling
diff --git a/internal/tasks/tasks.go b/internal/tasks/tasks.go
index 2c7dabb..393ec59 100644
--- a/internal/tasks/tasks.go
+++ b/internal/tasks/tasks.go
@@ -332,7 +332,7 @@ Apply safe updates directly, and leave concise follow-ups for anything uncertain
 		Type:            TaskCommitNormalize,
 		Category:        CategoryPR,
 		Name:            "Commit Message Normalizer",
-		Description:     "Standardize commit message format",
+		Description:     "Enforce repository commit message conventions via a git hook",
 		CostTier:        CostLow,
 		RiskLevel:       RiskLow,
 		DefaultInterval: 24 * time.Hour,
diff --git a/scripts/commit-msg.sh b/scripts/commit-msg.sh
new file mode 100755
index 0000000..c234d07
--- /dev/null
+++ b/scripts/commit-msg.sh
@@ -0,0 +1,101 @@
+#!/usr/bin/env bash
+# commit-msg hook for nightshift
+# Install: make install-hooks  (or: ln -sf ../../scripts/commit-msg.sh .git/hooks/commit-msg)
+set -euo pipefail
+
+MSG_FILE=${1:-}
+if [[ -z "$MSG_FILE" || ! -f "$MSG_FILE" ]]; then
+  echo "commit-msg: missing commit message file" >&2
+  exit 1
+fi
+
+TYPES="feat|fix|docs|test|refactor|chore|build|ci|perf|style|revert"
+SUBJECT_MAX=72
+
+trim() {
+  local value=$1
+  value="${value#"${value%%[![:space:]]*}"}"
+  value="${value%"${value##*[![:space:]]}"}"
+  printf '%s' "$value"
+}
+
+subject_line_number=$(
+  awk '
+    /^[[:space:]]*#/ { next }
+    /^[[:space:]]*$/ { next }
+    { print NR; exit }
+  ' "$MSG_FILE"
+)
+
+if [[ -z "$subject_line_number" ]]; then
+  echo "commit-msg: empty commit message" >&2
+  exit 1
+fi
+
+subject=$(
+  awk -v line="$subject_line_number" 'NR == line { print; exit }' "$MSG_FILE"
+)
+subject=$(trim "$subject")
+
+allow_special=false
+case "$subject" in
+  Merge\ *|Revert\ *|fixup!\ *|squash!\ *)
+    allow_special=true
+    ;;
+esac
+
+normalized=$subject
+if [[ "$allow_special" == false ]]; then
+  if [[ "$normalized" =~ ^([A-Za-z]+)(\([A-Za-z0-9._/-]+\))?[[:space:]]*[-:][[:space:]]*(.+)$ ]]; then
+    type_part=$(printf '%s' "${BASH_REMATCH[1]}" | tr '[:upper:]' '[:lower:]')
+    scope_part=${BASH_REMATCH[2]:-}
+    summary_part=$(trim "${BASH_REMATCH[3]}")
+    normalized="${type_part}${scope_part}: ${summary_part}"
+  fi
+fi
+
+if [[ "$normalized" != "$subject" ]]; then
+  tmp=$(mktemp)
+  awk -v line="$subject_line_number" -v replacement="$normalized" '
+    NR == line { print replacement; next }
+    { print }
+  ' "$MSG_FILE" > "$tmp"
+  cat "$tmp" > "$MSG_FILE"
+  rm -f "$tmp"
+  subject=$normalized
+fi
+
+if [[ "$allow_special" == true ]]; then
+  exit 0
+fi
+
+if ! [[ "$subject" =~ ^($TYPES)(\([A-Za-z0-9._/-]+\))?:[[:space:]][^[:space:]].*$ ]]; then
+  cat >&2 <<'EOF'
+commit-msg: expected commit message format:
+  type: summary
+  type(scope): summary
+
+Accepted types:
+  feat, fix, docs, test, refactor, chore, build, ci, perf, style, revert
+
+Examples:
+  feat: add project setup command
+  fix(config): preserve default provider
+  docs: document hook installation
+
+Merge, Revert, fixup!, and squash! commits are allowed.
+EOF
+  exit 1
+fi
+
+summary=${subject#*: }
+if [[ -z "$(trim "$summary")" ]]; then
+  echo "commit-msg: summary must not be empty" >&2
+  exit 1
+fi
+
+if (( ${#subject} > SUBJECT_MAX )); then
+  echo "commit-msg: subject must be ${SUBJECT_MAX} characters or fewer" >&2
+  echo "  ${subject}" >&2
+  exit 1
+fi