diff --git a/.githooks/commit-msg b/.githooks/commit-msg
new file mode 100755
index 0000000..dbe5a25
--- /dev/null
+++ b/.githooks/commit-msg
@@ -0,0 +1,24 @@
+#!/bin/sh
+# commit-msg hook — invoke the commit message normalizer.
+#
+# Enable for this repo:
+#   git config core.hooksPath .githooks
+# Or run: scripts/setup-hooks.sh
+
+set -e
+
+REPO_ROOT=$(git rev-parse --show-toplevel 2>/dev/null || pwd)
+NORMALIZER="$REPO_ROOT/scripts/commit-normalizer.sh"
+
+if [ ! -x "$NORMALIZER" ]; then
+    echo "commit-msg: normalizer not executable at $NORMALIZER" >&2
+    echo "  fix: chmod +x scripts/commit-normalizer.sh" >&2
+    exit 1
+fi
+
+# Allow opt-out for emergencies: COMMIT_NORMALIZER=0 git commit ...
+if [ "${COMMIT_NORMALIZER:-1}" = "0" ]; then
+    exit 0
+fi
+
+exec "$NORMALIZER" "$1"
diff --git a/.gitmessage b/.gitmessage
new file mode 100644
index 0000000..b5d8778
--- /dev/null
+++ b/.gitmessage
@@ -0,0 +1,36 @@
+# <type>(<scope>): <subject>   ── 72 chars or fewer; imperative mood
+#
+# Allowed types:
+#   feat      ── new feature
+#   fix       ── bug fix
+#   docs      ── documentation only
+#   style     ── formatting; no code change
+#   refactor  ── code change that neither fixes a bug nor adds a feature
+#   perf      ── performance improvement
+#   test      ── adding or correcting tests
+#   build     ── build system or dependency change
+#   ci        ── CI configuration change
+#   chore     ── housekeeping; no production code change
+#   revert    ── reverts a previous commit
+#
+# Scope is optional; use it for the affected area (e.g. parser, daemon).
+# Append `!` after the type/scope to mark a breaking change.
+#
+# Examples:
+#   feat(parser): allow optional trailing comma
+#   fix: handle empty config without panicking
+#   refactor(daemon)!: replace polling with channel-based notify
+#
+# ── Body ──────────────────────────────────────────────────────────────
+# Wrap at 72 chars. Explain *why* the change is needed; the diff already
+# shows *what* changed. Reference issues with `Fixes #123` or `Refs #45`.
+#
+#
+# ── Trailers ──────────────────────────────────────────────────────────
+# Use a single blank line before trailers. Common ones:
+#   Co-Authored-By: Name <email@example.com>
+#   Fixes: #123
+#   Refs: #45
+#   Signed-off-by: Name <email@example.com>
+#   Nightshift-Task: <task-id>
+#   Nightshift-Ref:  <task-url>
diff --git a/Makefile b/Makefile
index 088be01..ad09fb6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-.PHONY: build test test-verbose test-race coverage coverage-html lint clean deps check install calibrate-providers install-hooks help
+.PHONY: build test test-verbose test-race coverage coverage-html lint clean deps check install calibrate-providers install-hooks setup-hooks test-commit-normalizer help
 
 # Binary name
 BINARY=nightshift
@@ -76,9 +76,19 @@ help:
 	@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 "  setup-hooks    - Configure core.hooksPath + commit.template (commit-msg normalizer)"
+	@echo "  test-commit-normalizer - Run commit-msg normalizer fixture tests"
 	@echo "  help          - Show this help"
 
 # Install git pre-commit hook
 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)"
+
+# Configure repo-tracked git hooks (.githooks) and commit template
+setup-hooks:
+	@./scripts/setup-hooks.sh
+
+# Run commit-msg normalizer fixture tests
+test-commit-normalizer:
+	@./tests/commit-normalizer/run-tests.sh
diff --git a/docs/commit-conventions.md b/docs/commit-conventions.md
new file mode 100644
index 0000000..752208f
--- /dev/null
+++ b/docs/commit-conventions.md
@@ -0,0 +1,102 @@
+# Commit Message Conventions
+
+Nightshift uses [Conventional Commits](https://www.conventionalcommits.org/) for
+all commit messages. A local git hook normalizes and validates each message,
+so most contributors never need to think about formatting beyond following the
+template.
+
+## Format
+
+```
+<type>(<scope>)!: <subject>
+
+<body — optional, wrap at 72 chars>
+
+<trailers — optional>
+```
+
+- **type** *(required)* — one of: `feat`, `fix`, `docs`, `style`, `refactor`,
+  `perf`, `test`, `build`, `ci`, `chore`, `revert`.
+- **scope** *(optional)* — the area touched (`parser`, `daemon`, `config`).
+- **`!`** *(optional)* — appended to the type/scope to mark a breaking change.
+- **subject** *(required)* — imperative, no trailing period, ≤ 72 characters
+  including the type prefix.
+- **body** *(optional)* — separated from the subject by a blank line. Explain
+  *why* the change is needed.
+- **trailers** *(optional)* — `Key: value` lines after a blank line. Common
+  trailers: `Co-Authored-By`, `Fixes`, `Refs`, `Signed-off-by`,
+  `Nightshift-Task`, `Nightshift-Ref`.
+
+## Examples
+
+Valid:
+
+```
+feat(parser): allow optional trailing comma
+```
+
+```
+fix: handle empty config without panicking
+
+When NIGHTSHIFT_CONFIG points at an empty file the daemon crashed on
+startup. Treat empty as "use defaults".
+
+Fixes: #123
+```
+
+```
+refactor(daemon)!: replace polling with channel-based notify
+
+BREAKING CHANGE: the `--poll-interval` flag is removed. Configure
+notifications via `notify.channel` in the config file instead.
+```
+
+Invalid (and how the normalizer reacts):
+
+| Message                                | What happens                                      |
+| -------------------------------------- | ------------------------------------------------- |
+| `Fix typo`                             | Rejected — missing type prefix.                   |
+| `FEAT: add thing`                      | Normalized → `feat: add thing` (lowercased type). |
+| `feat:   add   thing  `                | Normalized — extra whitespace trimmed.            |
+| `wibble: do stuff`                     | Rejected — `wibble` is not an allowed type.       |
+| `feat: ` *(empty description)*         | Rejected — subject has no description.            |
+| 90-character `feat: …` subject          | Rejected — exceeds 72-char limit.                 |
+
+## Skip rules
+
+The normalizer intentionally leaves these alone:
+
+- Merge commits (`Merge branch …`, `Merge pull request …`).
+- Fixup / squash / amend commits (`fixup!`, `squash!`, `amend!`).
+- Revert commits (`Revert "…"`).
+
+## Enabling the hook
+
+Run once per clone:
+
+```sh
+scripts/setup-hooks.sh
+```
+
+This sets `core.hooksPath=.githooks` and `commit.template=.gitmessage`. After
+that, every `git commit` runs through `scripts/commit-normalizer.sh`.
+
+To bypass for a single commit:
+
+```sh
+COMMIT_NORMALIZER=0 git commit -m "..."
+```
+
+To disable entirely:
+
+```sh
+git config --unset core.hooksPath
+```
+
+## Testing the normalizer
+
+```sh
+tests/commit-normalizer/run-tests.sh
+```
+
+Fixture-driven; each case lives under `tests/commit-normalizer/cases/`.
diff --git a/scripts/commit-normalizer.sh b/scripts/commit-normalizer.sh
new file mode 100755
index 0000000..7692737
--- /dev/null
+++ b/scripts/commit-normalizer.sh
@@ -0,0 +1,184 @@
+#!/bin/sh
+# commit-normalizer.sh — language-agnostic Conventional Commits normalizer.
+#
+# Reads a commit message file, validates and normalizes its first line to
+# Conventional Commits format `<type>(<scope>)!: <subject>` (scope and `!`
+# optional), trims trailing whitespace, lowercases the type, and preserves
+# the body and trailer block intact.
+#
+# Exit codes:
+#   0 — message normalized (or intentionally skipped)
+#   1 — unfixable violation (caller should reject the commit)
+#   2 — usage error
+#
+# Skip rules: merge commits, fixup!/squash! commits, revert commits, and
+# messages that already begin with "Revert " are left untouched.
+
+set -eu
+
+PROG=$(basename "$0")
+
+usage() {
+    cat >&2 <<EOF
+Usage: $PROG <commit-message-file>
+
+Reads the file, normalizes the commit subject to Conventional Commits, and
+writes the result back in place. Exits non-zero on unfixable violations.
+EOF
+    exit 2
+}
+
+[ "$#" -eq 1 ] || usage
+MSG_FILE=$1
+[ -f "$MSG_FILE" ] || { echo "$PROG: not a file: $MSG_FILE" >&2; exit 2; }
+
+# Subject length limit (configurable via env).
+MAX_SUBJECT_LEN=${COMMIT_NORMALIZER_MAX_SUBJECT:-72}
+
+# Allowed Conventional Commits types.
+ALLOWED_TYPES="feat fix docs style refactor perf test build ci chore revert"
+
+# Read the file, stripping comment lines (git's scissor lines start with '#').
+RAW=$(awk '!/^#/' "$MSG_FILE")
+
+# Determine the first non-empty line — that's the subject candidate.
+SUBJECT=$(printf '%s\n' "$RAW" | awk 'NF { print; exit }')
+
+# Strip CR (Windows line endings) and trailing whitespace from the subject.
+SUBJECT=$(printf '%s' "$SUBJECT" | tr -d '\r' | sed 's/[[:space:]]*$//')
+
+# Skip rules — leave the message untouched.
+case "$SUBJECT" in
+    "Merge "*|"Merge branch "*|"Merge remote-tracking "*|"Merge pull request "*)
+        exit 0 ;;
+    "fixup! "*|"squash! "*|"amend! "*)
+        exit 0 ;;
+    "Revert "*|"revert: "*)
+        # Revert commits keep their auto-generated subject.
+        exit 0 ;;
+    "")
+        echo "$PROG: empty commit message" >&2
+        exit 1 ;;
+esac
+
+# Parse the subject into type, scope (optional), breaking marker, body.
+# Pattern:  type(scope)!: subject   |   type!: subject   |   type: subject
+PARSE=$(printf '%s' "$SUBJECT" | awk '
+    {
+        line = $0
+        # Capture optional leading type / scope / !.
+        if (match(line, /^[A-Za-z]+(\([^)]+\))?!?:[[:space:]]/)) {
+            header = substr(line, 1, RLENGTH)
+            rest   = substr(line, RLENGTH + 1)
+            # Split header into parts.
+            hd = header
+            sub(/:[[:space:]]*$/, "", hd)
+            bang = ""
+            if (hd ~ /!$/) { bang = "!"; sub(/!$/, "", hd) }
+            scope = ""
+            if (match(hd, /\([^)]+\)$/)) {
+                scope = substr(hd, RSTART + 1, RLENGTH - 2)
+                hd = substr(hd, 1, RSTART - 1)
+            }
+            type = hd
+            printf "%s\t%s\t%s\t%s\n", type, scope, bang, rest
+        } else {
+            printf "\t\t\t%s\n", line
+        }
+    }
+')
+
+TYPE=$(printf '%s' "$PARSE" | awk -F'\t' '{print $1}')
+SCOPE=$(printf '%s' "$PARSE" | awk -F'\t' '{print $2}')
+BANG=$(printf '%s' "$PARSE" | awk -F'\t' '{print $3}')
+BODY=$(printf '%s' "$PARSE" | awk -F'\t' '{print $4}')
+
+if [ -z "$TYPE" ]; then
+    cat >&2 <<EOF
+$PROG: subject is not Conventional Commits format
+  got:      $SUBJECT
+  expected: <type>(<scope>)!: <subject>
+  types:    $ALLOWED_TYPES
+  example:  feat(parser): allow optional trailing comma
+EOF
+    exit 1
+fi
+
+# Lowercase the type.
+TYPE=$(printf '%s' "$TYPE" | tr '[:upper:]' '[:lower:]')
+
+# Validate type.
+TYPE_OK=0
+for t in $ALLOWED_TYPES; do
+    if [ "$t" = "$TYPE" ]; then TYPE_OK=1; break; fi
+done
+if [ "$TYPE_OK" -ne 1 ]; then
+    cat >&2 <<EOF
+$PROG: unknown commit type "$TYPE"
+  allowed: $ALLOWED_TYPES
+EOF
+    exit 1
+fi
+
+# Trim leading whitespace from the body portion of the subject.
+BODY=$(printf '%s' "$BODY" | sed 's/^[[:space:]]*//; s/[[:space:]]*$//')
+
+if [ -z "$BODY" ]; then
+    echo "$PROG: subject has no description after '$TYPE:'" >&2
+    exit 1
+fi
+
+# Rebuild the normalized subject.
+if [ -n "$SCOPE" ]; then
+    NORMALIZED="$TYPE($SCOPE)$BANG: $BODY"
+else
+    NORMALIZED="$TYPE$BANG: $BODY"
+fi
+
+# Enforce subject length.
+SUBJECT_LEN=$(printf '%s' "$NORMALIZED" | awk '{print length}')
+if [ "$SUBJECT_LEN" -gt "$MAX_SUBJECT_LEN" ]; then
+    cat >&2 <<EOF
+$PROG: subject too long ($SUBJECT_LEN > $MAX_SUBJECT_LEN chars)
+  subject: $NORMALIZED
+  tip:     move detail into the body (blank line, then explanation)
+EOF
+    exit 1
+fi
+
+# Reassemble the message: normalized subject + remaining lines after the
+# original subject. We preserve the body and trailer block byte-for-byte
+# (minus trailing whitespace per line). Comment lines from git templates
+# are stripped — git would do this anyway.
+TMP=$(mktemp "${TMPDIR:-/tmp}/commit-normalizer.XXXXXX")
+trap 'rm -f "$TMP"' EXIT INT TERM
+
+awk -v normalized="$NORMALIZED" '
+    BEGIN { subject_done = 0 }
+    /^#/  { next }
+    {
+        if (!subject_done && $0 ~ /[^[:space:]]/) {
+            print normalized
+            subject_done = 1
+            next
+        }
+        # Strip trailing whitespace from every line.
+        sub(/[[:space:]]+$/, "", $0)
+        print
+    }
+' "$MSG_FILE" > "$TMP"
+
+# Collapse trailing blank lines down to one terminating newline.
+awk '
+    { lines[NR] = $0 }
+    END {
+        n = NR
+        while (n > 0 && lines[n] == "") n--
+        for (i = 1; i <= n; i++) print lines[i]
+    }
+' "$TMP" > "$TMP.2"
+mv "$TMP.2" "$MSG_FILE"
+rm -f "$TMP"
+trap - EXIT INT TERM
+
+exit 0
diff --git a/scripts/setup-hooks.sh b/scripts/setup-hooks.sh
new file mode 100755
index 0000000..6829a04
--- /dev/null
+++ b/scripts/setup-hooks.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+# setup-hooks.sh — configure local git to use repo-tracked hooks.
+#
+# Sets `core.hooksPath` to .githooks and `commit.template` to .gitmessage so
+# that the commit-msg normalizer runs and contributors see the template when
+# they `git commit` without `-m`.
+
+set -eu
+
+REPO_ROOT=$(git rev-parse --show-toplevel 2>/dev/null) || {
+    echo "setup-hooks: not inside a git repository" >&2
+    exit 1
+}
+
+cd "$REPO_ROOT"
+
+chmod +x .githooks/commit-msg scripts/commit-normalizer.sh 2>/dev/null || true
+
+git config core.hooksPath .githooks
+git config commit.template .gitmessage
+
+cat <<EOF
+✓ core.hooksPath  = .githooks
+✓ commit.template = .gitmessage
+
+The commit-msg hook will normalize messages to Conventional Commits.
+See docs/commit-conventions.md for the full standard.
+
+To bypass once:   COMMIT_NORMALIZER=0 git commit -m "..."
+To disable:       git config --unset core.hooksPath
+EOF
diff --git a/tests/commit-normalizer/cases/01-valid-conventional/expected b/tests/commit-normalizer/cases/01-valid-conventional/expected
new file mode 100644
index 0000000..f54e832
--- /dev/null
+++ b/tests/commit-normalizer/cases/01-valid-conventional/expected
@@ -0,0 +1,5 @@
+feat(parser): allow optional trailing comma
+
+Trailing commas in function arguments simplify diffs.
+
+Refs: #42
diff --git a/tests/commit-normalizer/cases/01-valid-conventional/input b/tests/commit-normalizer/cases/01-valid-conventional/input
new file mode 100644
index 0000000..f54e832
--- /dev/null
+++ b/tests/commit-normalizer/cases/01-valid-conventional/input
@@ -0,0 +1,5 @@
+feat(parser): allow optional trailing comma
+
+Trailing commas in function arguments simplify diffs.
+
+Refs: #42
diff --git a/tests/commit-normalizer/cases/02-missing-type/exit b/tests/commit-normalizer/cases/02-missing-type/exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/commit-normalizer/cases/02-missing-type/exit
@@ -0,0 +1 @@
+1
diff --git a/tests/commit-normalizer/cases/02-missing-type/expected.err b/tests/commit-normalizer/cases/02-missing-type/expected.err
new file mode 100644
index 0000000..1ddd2d3
--- /dev/null
+++ b/tests/commit-normalizer/cases/02-missing-type/expected.err
@@ -0,0 +1 @@
+not Conventional Commits format
\ No newline at end of file
diff --git a/tests/commit-normalizer/cases/02-missing-type/input b/tests/commit-normalizer/cases/02-missing-type/input
new file mode 100644
index 0000000..e0051b4
--- /dev/null
+++ b/tests/commit-normalizer/cases/02-missing-type/input
@@ -0,0 +1 @@
+just fix the thing
diff --git a/tests/commit-normalizer/cases/03-oversized-subject/exit b/tests/commit-normalizer/cases/03-oversized-subject/exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/commit-normalizer/cases/03-oversized-subject/exit
@@ -0,0 +1 @@
+1
diff --git a/tests/commit-normalizer/cases/03-oversized-subject/expected.err b/tests/commit-normalizer/cases/03-oversized-subject/expected.err
new file mode 100644
index 0000000..1d4f3cf
--- /dev/null
+++ b/tests/commit-normalizer/cases/03-oversized-subject/expected.err
@@ -0,0 +1 @@
+subject too long
\ No newline at end of file
diff --git a/tests/commit-normalizer/cases/03-oversized-subject/input b/tests/commit-normalizer/cases/03-oversized-subject/input
new file mode 100644
index 0000000..7bddb05
--- /dev/null
+++ b/tests/commit-normalizer/cases/03-oversized-subject/input
@@ -0,0 +1 @@
+feat: this is an extraordinarily long subject line that goes on and on far past the seventy-two character ceiling we picked
diff --git a/tests/commit-normalizer/cases/04-mixed-case-type/expected b/tests/commit-normalizer/cases/04-mixed-case-type/expected
new file mode 100644
index 0000000..d5a6414
--- /dev/null
+++ b/tests/commit-normalizer/cases/04-mixed-case-type/expected
@@ -0,0 +1 @@
+feat(API): add health endpoint
diff --git a/tests/commit-normalizer/cases/04-mixed-case-type/input b/tests/commit-normalizer/cases/04-mixed-case-type/input
new file mode 100644
index 0000000..3239517
--- /dev/null
+++ b/tests/commit-normalizer/cases/04-mixed-case-type/input
@@ -0,0 +1 @@
+FEAT(API): add health endpoint
diff --git a/tests/commit-normalizer/cases/05-trailing-whitespace/expected b/tests/commit-normalizer/cases/05-trailing-whitespace/expected
new file mode 100644
index 0000000..4c87668
--- /dev/null
+++ b/tests/commit-normalizer/cases/05-trailing-whitespace/expected
@@ -0,0 +1,6 @@
+fix: handle empty config without panicking
+
+When NIGHTSHIFT_CONFIG is empty the daemon crashed.
+Treat empty as "use defaults".
+
+Fixes: #123
diff --git a/tests/commit-normalizer/cases/05-trailing-whitespace/input b/tests/commit-normalizer/cases/05-trailing-whitespace/input
new file mode 100644
index 0000000..f99ba5a
--- /dev/null
+++ b/tests/commit-normalizer/cases/05-trailing-whitespace/input
@@ -0,0 +1,6 @@
+fix:   handle empty config without panicking
+
+When NIGHTSHIFT_CONFIG is empty the daemon crashed.
+Treat empty as "use defaults".
+
+Fixes: #123
diff --git a/tests/commit-normalizer/cases/06-preserved-trailers/expected b/tests/commit-normalizer/cases/06-preserved-trailers/expected
new file mode 100644
index 0000000..a3616a2
--- /dev/null
+++ b/tests/commit-normalizer/cases/06-preserved-trailers/expected
@@ -0,0 +1,9 @@
+feat(daemon): add notify channel
+
+Switch from polling to channel-based notifications.
+
+Co-Authored-By: Alice <alice@example.com>
+Co-Authored-By: Bob <bob@example.com>
+Nightshift-Task: commit-normalize
+Nightshift-Ref: https://github.com/marcus/nightshift
+Signed-off-by: Carol <carol@example.com>
diff --git a/tests/commit-normalizer/cases/06-preserved-trailers/input b/tests/commit-normalizer/cases/06-preserved-trailers/input
new file mode 100644
index 0000000..a3616a2
--- /dev/null
+++ b/tests/commit-normalizer/cases/06-preserved-trailers/input
@@ -0,0 +1,9 @@
+feat(daemon): add notify channel
+
+Switch from polling to channel-based notifications.
+
+Co-Authored-By: Alice <alice@example.com>
+Co-Authored-By: Bob <bob@example.com>
+Nightshift-Task: commit-normalize
+Nightshift-Ref: https://github.com/marcus/nightshift
+Signed-off-by: Carol <carol@example.com>
diff --git a/tests/commit-normalizer/cases/07-merge-commit-skipped/expected b/tests/commit-normalizer/cases/07-merge-commit-skipped/expected
new file mode 100644
index 0000000..2d5606d
--- /dev/null
+++ b/tests/commit-normalizer/cases/07-merge-commit-skipped/expected
@@ -0,0 +1 @@
+Merge branch 'develop' into main
diff --git a/tests/commit-normalizer/cases/07-merge-commit-skipped/input b/tests/commit-normalizer/cases/07-merge-commit-skipped/input
new file mode 100644
index 0000000..2d5606d
--- /dev/null
+++ b/tests/commit-normalizer/cases/07-merge-commit-skipped/input
@@ -0,0 +1 @@
+Merge branch 'develop' into main
diff --git a/tests/commit-normalizer/cases/08-fixup-commit-skipped/expected b/tests/commit-normalizer/cases/08-fixup-commit-skipped/expected
new file mode 100644
index 0000000..5b9fc7b
--- /dev/null
+++ b/tests/commit-normalizer/cases/08-fixup-commit-skipped/expected
@@ -0,0 +1 @@
+fixup! feat(parser): allow optional trailing comma
diff --git a/tests/commit-normalizer/cases/08-fixup-commit-skipped/input b/tests/commit-normalizer/cases/08-fixup-commit-skipped/input
new file mode 100644
index 0000000..5b9fc7b
--- /dev/null
+++ b/tests/commit-normalizer/cases/08-fixup-commit-skipped/input
@@ -0,0 +1 @@
+fixup! feat(parser): allow optional trailing comma
diff --git a/tests/commit-normalizer/cases/09-unknown-type/exit b/tests/commit-normalizer/cases/09-unknown-type/exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/commit-normalizer/cases/09-unknown-type/exit
@@ -0,0 +1 @@
+1
diff --git a/tests/commit-normalizer/cases/09-unknown-type/expected.err b/tests/commit-normalizer/cases/09-unknown-type/expected.err
new file mode 100644
index 0000000..7bfcb44
--- /dev/null
+++ b/tests/commit-normalizer/cases/09-unknown-type/expected.err
@@ -0,0 +1 @@
+unknown commit type
\ No newline at end of file
diff --git a/tests/commit-normalizer/cases/09-unknown-type/input b/tests/commit-normalizer/cases/09-unknown-type/input
new file mode 100644
index 0000000..3e41700
--- /dev/null
+++ b/tests/commit-normalizer/cases/09-unknown-type/input
@@ -0,0 +1 @@
+wibble: do mysterious things
diff --git a/tests/commit-normalizer/cases/10-breaking-change/expected b/tests/commit-normalizer/cases/10-breaking-change/expected
new file mode 100644
index 0000000..54c30ef
--- /dev/null
+++ b/tests/commit-normalizer/cases/10-breaking-change/expected
@@ -0,0 +1,3 @@
+refactor(daemon)!: replace polling with channel notify
+
+BREAKING CHANGE: --poll-interval is removed.
diff --git a/tests/commit-normalizer/cases/10-breaking-change/input b/tests/commit-normalizer/cases/10-breaking-change/input
new file mode 100644
index 0000000..54c30ef
--- /dev/null
+++ b/tests/commit-normalizer/cases/10-breaking-change/input
@@ -0,0 +1,3 @@
+refactor(daemon)!: replace polling with channel notify
+
+BREAKING CHANGE: --poll-interval is removed.
diff --git a/tests/commit-normalizer/cases/11-strip-comments/expected b/tests/commit-normalizer/cases/11-strip-comments/expected
new file mode 100644
index 0000000..c66289c
--- /dev/null
+++ b/tests/commit-normalizer/cases/11-strip-comments/expected
@@ -0,0 +1,4 @@
+feat: support TOML config
+
+
+Adds a parallel TOML loader alongside YAML.
diff --git a/tests/commit-normalizer/cases/11-strip-comments/input b/tests/commit-normalizer/cases/11-strip-comments/input
new file mode 100644
index 0000000..f369a0f
--- /dev/null
+++ b/tests/commit-normalizer/cases/11-strip-comments/input
@@ -0,0 +1,8 @@
+feat: support TOML config
+
+# Please enter the commit message for your changes. Lines starting
+# with '#' will be ignored, and an empty message aborts the commit.
+#
+# On branch feature/x
+
+Adds a parallel TOML loader alongside YAML.
diff --git a/tests/commit-normalizer/cases/12-empty-description/exit b/tests/commit-normalizer/cases/12-empty-description/exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/commit-normalizer/cases/12-empty-description/exit
@@ -0,0 +1 @@
+1
diff --git a/tests/commit-normalizer/cases/12-empty-description/expected.err b/tests/commit-normalizer/cases/12-empty-description/expected.err
new file mode 100644
index 0000000..1ddd2d3
--- /dev/null
+++ b/tests/commit-normalizer/cases/12-empty-description/expected.err
@@ -0,0 +1 @@
+not Conventional Commits format
\ No newline at end of file
diff --git a/tests/commit-normalizer/cases/12-empty-description/input b/tests/commit-normalizer/cases/12-empty-description/input
new file mode 100644
index 0000000..36353fd
--- /dev/null
+++ b/tests/commit-normalizer/cases/12-empty-description/input
@@ -0,0 +1 @@
+feat:
diff --git a/tests/commit-normalizer/run-tests.sh b/tests/commit-normalizer/run-tests.sh
new file mode 100755
index 0000000..c0624e2
--- /dev/null
+++ b/tests/commit-normalizer/run-tests.sh
@@ -0,0 +1,89 @@
+#!/bin/sh
+# run-tests.sh — fixture-driven tests for scripts/commit-normalizer.sh.
+#
+# Each case directory under tests/commit-normalizer/cases/ may contain:
+#   input          — the commit message to feed the normalizer
+#   expected       — the expected normalized output (if exit is 0)
+#   exit           — expected exit code (default 0)
+#   expected.err   — substring expected on stderr (optional)
+
+set -eu
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+REPO_ROOT=$(cd "$SCRIPT_DIR/../.." && pwd)
+NORMALIZER="$REPO_ROOT/scripts/commit-normalizer.sh"
+CASES_DIR="$SCRIPT_DIR/cases"
+
+[ -x "$NORMALIZER" ] || chmod +x "$NORMALIZER"
+
+PASS=0
+FAIL=0
+FAIL_NAMES=""
+
+for case_dir in "$CASES_DIR"/*/; do
+    name=$(basename "$case_dir")
+    input="$case_dir/input"
+    [ -f "$input" ] || { echo "skip: $name (no input)"; continue; }
+
+    expected_exit=0
+    [ -f "$case_dir/exit" ] && expected_exit=$(cat "$case_dir/exit")
+
+    work=$(mktemp "${TMPDIR:-/tmp}/cn-test.XXXXXX")
+    err=$(mktemp "${TMPDIR:-/tmp}/cn-test-err.XXXXXX")
+    cp "$input" "$work"
+
+    set +e
+    "$NORMALIZER" "$work" 2>"$err"
+    got_exit=$?
+    set -e
+
+    ok=1
+    msg=""
+
+    if [ "$got_exit" -ne "$expected_exit" ]; then
+        ok=0
+        msg="exit $got_exit, expected $expected_exit"
+    fi
+
+    if [ "$ok" -eq 1 ] && [ "$expected_exit" -eq 0 ] && [ -f "$case_dir/expected" ]; then
+        if ! diff -u "$case_dir/expected" "$work" >/dev/null; then
+            ok=0
+            msg="output mismatch"
+            DIFF=$(diff -u "$case_dir/expected" "$work" || true)
+        fi
+    fi
+
+    if [ "$ok" -eq 1 ] && [ -f "$case_dir/expected.err" ]; then
+        needle=$(cat "$case_dir/expected.err")
+        if ! grep -qF "$needle" "$err"; then
+            ok=0
+            msg="stderr missing: $needle"
+        fi
+    fi
+
+    if [ "$ok" -eq 1 ]; then
+        printf "  ✓ %s\n" "$name"
+        PASS=$((PASS + 1))
+    else
+        printf "  ✗ %s — %s\n" "$name" "$msg"
+        if [ -n "${DIFF:-}" ]; then
+            printf '%s\n' "$DIFF" | sed 's/^/      /'
+            DIFF=""
+        fi
+        if [ -s "$err" ]; then
+            printf "    stderr:\n"
+            sed 's/^/      /' "$err"
+        fi
+        FAIL=$((FAIL + 1))
+        FAIL_NAMES="$FAIL_NAMES $name"
+    fi
+
+    rm -f "$work" "$err"
+done
+
+echo
+echo "passed: $PASS  failed: $FAIL"
+if [ "$FAIL" -gt 0 ]; then
+    echo "failures:$FAIL_NAMES"
+    exit 1
+fi