diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3b53794b..5733dab3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -53,12 +53,5 @@ jobs:
           persist-credentials: false
       - uses: taiki-e/install-action@shellcheck
       - uses: taiki-e/install-action@shfmt
-      - run: npm install prettier
-      - run: shfmt -d $(git ls-files '*.sh')
-        if: always()
-      - run: npx prettier -c $(git ls-files '*.yml')
-        if: always()
-      - run: npx prettier -c $(git ls-files '*.js')
-        if: always()
-      - run: shellcheck $(git ls-files '*.sh')
+      - run: tools/tidy.sh
         if: always()
diff --git a/tools/publish.sh b/tools/publish.sh
index c998b394..745c4b38 100755
--- a/tools/publish.sh
+++ b/tools/publish.sh
@@ -8,8 +8,8 @@ cd "$(dirname "$0")"/..
 # USAGE:
 #    ./tools/publish.sh <VERSION>
 #
-# Note:
-# - This script requires parse-changelog <https://github.com/taiki-e/parse-changelog>
+# Note: This script requires the following tools:
+# - parse-changelog <https://github.com/taiki-e/parse-changelog>
 
 bail() {
     echo >&2 "error: $*"
diff --git a/tools/tidy.sh b/tools/tidy.sh
index 78e9af05..c702532f 100755
--- a/tools/tidy.sh
+++ b/tools/tidy.sh
@@ -9,8 +9,14 @@ cd "$(dirname "$0")"/..
 #
 # Note: This script requires the following tools:
 # - shfmt
-# - prettier
 # - shellcheck
+# - npm (if any of YAML/JavaScript/JSON exists)
+# - jq and yq (if this repository uses bors)
+# - clang-format (if any of C/C++ exists)
+#
+# This script is shared with other repositories, so there may also be
+# checks for files not included in this repository, but they will be
+# skipped if the corresponding files do not exist.
 
 x() {
     local cmd="$1"
@@ -24,14 +30,33 @@ x() {
         "${cmd}" "$@"
     fi
 }
+check_diff() {
+    if [[ -n "${CI:-}" ]]; then
+        if ! git --no-pager diff --exit-code "$@"; then
+            should_fail=1
+        fi
+    else
+        if ! git --no-pager diff --exit-code "$@" &>/dev/null; then
+            should_fail=1
+        fi
+    fi
+}
 warn() {
-    echo >&2 "warning: $*"
+    if [[ -n "${GITHUB_ACTIONS:-}" ]]; then
+        echo "::warning::$*"
+    else
+        echo >&2 "warning: $*"
+    fi
+    should_fail=1
 }
 
 if [[ "${1:-}" == "-v" ]]; then
     shift
     verbose=1
 fi
+if [[ -n "${CI:-}" ]]; then
+    verbose=1
+fi
 if [[ $# -gt 0 ]]; then
     cat <<EOF
 USAGE:
@@ -40,24 +65,74 @@ EOF
     exit 1
 fi
 
-prettier=prettier
-if type -P npm &>/dev/null && type -P "$(npm bin)/prettier" &>/dev/null; then
-    prettier="$(npm bin)/prettier"
+# C/C++ (if exists)
+if [[ -n "$(git ls-files '*.c')$(git ls-files '*.cpp')" ]]; then
+    if [[ ! -e .clang-format ]]; then
+        warn "could not fount .clang-format in the repository root"
+    fi
+    if type -P clang-format &>/dev/null; then
+        x clang-format -i $(git ls-files '*.c') $(git ls-files '*.cpp')
+        check_diff $(git ls-files '*.c') $(git ls-files '*.cpp')
+    else
+        warn "'clang-format' is not installed"
+    fi
 fi
 
+# YAML/JavaScript/JSON (if exists)
+if [[ -n "$(git ls-files '*.yml')$(git ls-files '*.js')$(git ls-files '*.json')" ]]; then
+    if type -P npm &>/dev/null; then
+        if [[ ! -e node_modules/.bin/prettier ]]; then
+            x npm install prettier &>/dev/null
+        fi
+        x npx prettier -l -w $(git ls-files '*.yml') $(git ls-files '*.js') $(git ls-files '*.json')
+        check_diff $(git ls-files '*.yml') $(git ls-files '*.js') $(git ls-files '*.json')
+    else
+        warn "'npm' is not installed"
+    fi
+    if [[ -e .github/workflows/ci.yml ]] && grep -q '# tidy:needs' .github/workflows/ci.yml; then
+        if type -P jq &>/dev/null && type -P yq &>/dev/null; then
+            # shellcheck disable=SC2207
+            jobs_actual=($(yq '.jobs' .github/workflows/ci.yml | jq -r 'keys_unsorted[]'))
+            unset 'jobs_actual[${#jobs_actual[@]}-1]'
+            # shellcheck disable=SC2207
+            jobs_expected=($(yq -r '.jobs."ci-success".needs[]' .github/workflows/ci.yml))
+            if [[ "${jobs_actual[*]}" != "${jobs_expected[*]+"${jobs_expected[*]}"}" ]]; then
+                printf -v jobs '%s, ' "${jobs_actual[@]}"
+                sed -i "s/needs: \[.*\] # tidy:needs/needs: [${jobs%, }] # tidy:needs/" .github/workflows/ci.yml
+                check_diff .github/workflows/ci.yml
+                warn "please update 'needs' section in 'ci-success' job"
+            fi
+        else
+            warn "'jq' or 'yq' is not installed"
+        fi
+    fi
+fi
+if [[ -n "$(git ls-files '*.yaml')" ]]; then
+    warn "please use '.yml' instead of '.yaml' for consistency"
+    git ls-files '*.yaml'
+fi
+
+# Shell scripts
 if type -P shfmt &>/dev/null; then
     x shfmt -l -w $(git ls-files '*.sh')
+    check_diff $(git ls-files '*.sh')
 else
     warn "'shfmt' is not installed"
 fi
-if type -P "${prettier}" &>/dev/null; then
-    x "${prettier}" -l -w $(git ls-files '*.yml')
-    x "${prettier}" -l -w $(git ls-files '*.js')
-else
-    warn "'prettier' is not installed"
-fi
 if type -P shellcheck &>/dev/null; then
-    x shellcheck $(git ls-files '*.sh')
+    if ! x shellcheck $(git ls-files '*.sh'); then
+        should_fail=1
+    fi
+    if [[ -n "$(git ls-files '*Dockerfile')" ]]; then
+        # SC2154 doesn't seem to work on dockerfile.
+        if ! x shellcheck -e SC2148,SC2154,SC2250 $(git ls-files '*Dockerfile'); then
+            should_fail=1
+        fi
+    fi
 else
     warn "'shellcheck' is not installed"
 fi
+
+if [[ -n "${should_fail:-}" ]]; then
+    exit 1
+fi