diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8fc5686..64e4048 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,6 +7,50 @@ on:
     branches: [main]
 
 jobs:
+  commit-messages:
+    name: Commit Messages
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Validate commit messages
+        shell: bash
+        run: |
+          set -euo pipefail
+
+          if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+            base="${{ github.event.pull_request.base.sha }}"
+            head="${{ github.event.pull_request.head.sha }}"
+            merge_base="$(git merge-base "$base" "$head")"
+            range="$merge_base..$head"
+          else
+            before="${{ github.event.before }}"
+            if [[ "$before" == "0000000000000000000000000000000000000000" ]]; then
+              range="${{ github.sha }}^!"
+            else
+              range="$before..${{ github.sha }}"
+            fi
+          fi
+
+          commits="$(git rev-list --no-merges "$range")"
+          if [[ -z "$commits" ]]; then
+            echo "No non-merge commits to validate."
+            exit 0
+          fi
+
+          tmp="$(mktemp)"
+          trap 'rm -f "$tmp"' EXIT
+
+          while IFS= read -r commit; do
+            [[ -n "$commit" ]] || continue
+            git show -s --format=%B "$commit" > "$tmp"
+            echo "check $commit"
+            scripts/commit-msg.sh "$tmp"
+          done <<< "$commits"
+
   test:
     name: Test
     runs-on: ubuntu-latest
diff --git a/Makefile b/Makefile
index 088be01..73b5464 100644
--- a/Makefile
+++ b/Makefile
@@ -75,10 +75,24 @@ 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 pre-commit and commit-msg hook wrappers"
 	@echo "  help          - Show this help"
 
-# Install git pre-commit hook
+# Install git hook wrappers
 install-hooks:
-	@ln -sf ../../scripts/pre-commit.sh .git/hooks/pre-commit
-	@echo "✓ pre-commit hook installed (.git/hooks/pre-commit → scripts/pre-commit.sh)"
+	@hooks_dir="$$(git rev-parse --git-path hooks)"; \
+	mkdir -p "$$hooks_dir"; \
+	for hook in pre-commit commit-msg; do \
+		hook_path="$$hooks_dir/$$hook"; \
+		script_path="scripts/$$hook.sh"; \
+		rm -f "$$hook_path"; \
+		{ \
+			printf '%s\n' '#!/usr/bin/env bash'; \
+			printf '%s\n' 'set -euo pipefail'; \
+			printf '%s\n' 'repo_root="$$(git rev-parse --show-toplevel)"'; \
+			printf '%s\n' 'exec "$$repo_root/'"$$script_path"'" "$$@"'; \
+		} > "$$hook_path"; \
+		chmod +x "$$hook_path"; \
+		echo "✓ $$hook_path -> $$script_path"; \
+	done; \
+	echo "hooks installed with worktree-safe wrappers"
diff --git a/README.md b/README.md
index 84f92cd..26270e2 100644
--- a/README.md
+++ b/README.md
@@ -258,20 +258,60 @@ 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:
+Use `type(scope): summary` or `type: summary` for new commits. Allowed types:
+`build`, `chore`, `ci`, `docs`, `feat`, `fix`, `perf`, `refactor`,
+`revert`, `style`, `test`.
+
+Keep the summary short, imperative, and without a trailing period. If you add a
+body or trailers, leave line 2 blank.
+
+GitHub squash merges may append `(#123)` to the subject on `main`; that suffix
+is accepted, including `Revert "..." (#123)` subjects from revert PRs.
+
+Valid examples:
+
+```text
+fix: install commit-msg hook
+feat(tasks): add commit metadata trailers
+docs: explain contributor hook setup
+
+fix: normalize commit subjects
+
+Allow release and merge commit exemptions.
+
+Nightshift-Task: commit-normalize
+Nightshift-Ref: https://github.com/marcus/nightshift
+```
+
+Allowed exceptions:
+- Actual merge commits generated by Git
+- `Revert "..."` commits generated by `git revert`
+- Release/version commits like `Bump version to v0.3.5` or `Release v0.3.5: ...`
+
+### Git hooks
+
+Install the local git hooks before contributing:
 
 ```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
+This writes both hooks into Git's configured hooks directory as lightweight,
+worktree-safe wrappers. Each wrapper resolves the current worktree root at
+runtime, then runs:
+- `scripts/pre-commit.sh`
+- `scripts/commit-msg.sh`
+
+The hooks run:
+- **pre-commit** — `gofmt`, `go vet`, `go build`
+- **commit-msg** — validates the commit subject/body layout above
+
+CI runs the same commit-message validator for non-merge commits in PRs and
+pushes, so web edits or `--no-verify` commits still have to match the standard.
 
-To bypass in a pinch: `git commit --no-verify`
+To bypass the local hooks in a pinch: `git commit --no-verify`
 
 ## Uninstalling
 
diff --git a/scripts/commit-msg.sh b/scripts/commit-msg.sh
new file mode 100755
index 0000000..fc38cb9
--- /dev/null
+++ b/scripts/commit-msg.sh
@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# commit-msg hook for nightshift
+# Install: make install-hooks
+set -euo pipefail
+
+TYPES="build|chore|ci|docs|feat|fix|perf|refactor|revert|style|test"
+
+usage() {
+  echo "usage: $0 <commit-msg-file>" >&2
+  exit 1
+}
+
+fail() {
+  echo "commit-msg: $1" >&2
+  echo "use: type(scope): summary" >&2
+  echo "types: build|chore|ci|docs|feat|fix|perf|refactor|revert|style|test" >&2
+  echo 'exceptions: merge commits, Revert "...", Bump version..., Release v...' >&2
+  exit 1
+}
+
+[[ $# -eq 1 ]] || usage
+
+msg_file="$1"
+[[ -f "$msg_file" ]] || usage
+
+lines=()
+while IFS= read -r line || [[ -n "$line" ]]; do
+  line=${line%$'\r'}
+  if [[ "$line" =~ ^[[:space:]]*# ]]; then
+    continue
+  fi
+  lines+=("$line")
+done < "$msg_file"
+
+while [[ ${#lines[@]} -gt 0 ]]; do
+  last_index=$((${#lines[@]} - 1))
+  [[ -n "${lines[$last_index]}" ]] && break
+  unset 'lines[$last_index]'
+done
+
+[[ ${#lines[@]} -gt 0 ]] || fail "empty commit message"
+
+subject="${lines[0]}"
+subject_core="$subject"
+if [[ "$subject_core" =~ ^(.+)\ \(#[0-9]+\)$ ]]; then
+  subject_core="${BASH_REMATCH[1]}"
+fi
+
+merge_re='^Merge (branch|remote-tracking branch|pull request|tag) '
+revert_re='^Revert ".*"$'
+release_bump_re='^Bump version to v[0-9]+(\.[0-9]+)*([.-][A-Za-z0-9]+)*$'
+release_re='^Release v[0-9]+(\.[0-9]+)*([.-][A-Za-z0-9]+)*(: .+)?$'
+
+if git rev-parse -q --verify MERGE_HEAD >/dev/null 2>&1 || [[ "$subject" =~ $merge_re ]] || [[ "$subject_core" =~ $revert_re ]] || [[ "$subject_core" =~ $release_bump_re ]] || [[ "$subject_core" =~ $release_re ]]; then
+  exit 0
+fi
+
+subject_re="^(${TYPES})(\\([A-Za-z0-9#][A-Za-z0-9._/#-]*\\))?(!)?: .+$"
+[[ "$subject" =~ $subject_re ]] || fail "expected Conventional Commits subject"
+
+[[ "$subject_core" != *. ]] || fail "subject must not end with a period"
+
+if [[ ${#lines[@]} -gt 1 ]] && [[ -n "${lines[1]}" ]]; then
+  fail "leave line 2 blank before body or trailers"
+fi
diff --git a/scripts/pre-commit.sh b/scripts/pre-commit.sh
index c597d65..975f717 100755
--- a/scripts/pre-commit.sh
+++ b/scripts/pre-commit.sh
@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 # pre-commit hook for nightshift
-# Install: make install-hooks  (or: ln -sf ../../scripts/pre-commit.sh .git/hooks/pre-commit)
+# Install: make install-hooks
 set -euo pipefail
 
 PASS=0