diff --git a/bin/resolve-php-version.sh b/bin/resolve-php-version.sh
new file mode 100644
index 00000000..00bfd353
--- /dev/null
+++ b/bin/resolve-php-version.sh
@@ -0,0 +1,96 @@
+#!/usr/bin/env bash
+
+ENGINE="$1"
+
+has_node() {
+  command -v node > /dev/null 2>&1
+}
+
+get_default_version() {
+  case "$1" in
+    "evert/phpdoc-md")
+      echo "7.4"
+      ;;
+    "clean/phpdoc-md")
+      echo "8.1"
+      ;;
+    *)
+      echo "ERROR: unknown engine" >&2
+      return 1
+      ;;
+  esac
+}
+
+get_constraint_from_composer_json() {
+  if [ ! -f "composer.json" ] || ! has_node; then
+    return 0
+  fi
+
+  node -e "
+const fs = require('fs');
+try {
+  const data = JSON.parse(fs.readFileSync('composer.json', 'utf8'));
+  const requirePhp = data?.require?.php;
+  if (typeof requirePhp === 'string' && requirePhp.trim() !== '') {
+    process.stdout.write(requirePhp.trim());
+    process.exit(0);
+  }
+  const platformPhp = data?.config?.platform?.php;
+  if (typeof platformPhp === 'string' && platformPhp.trim() !== '') {
+    process.stdout.write(platformPhp.trim());
+  }
+} catch (_) {}
+"
+}
+
+get_constraint_from_composer_lock() {
+  if [ ! -f "composer.lock" ] || ! has_node; then
+    return 0
+  fi
+
+  node -e "
+const fs = require('fs');
+try {
+  const data = JSON.parse(fs.readFileSync('composer.lock', 'utf8'));
+  const platformPhp = data?.platform?.php;
+  if (typeof platformPhp === 'string' && platformPhp.trim() !== '') {
+    process.stdout.write(platformPhp.trim());
+    process.exit(0);
+  }
+  const overriddenPhp = data?.['platform-overrides']?.php;
+  if (typeof overriddenPhp === 'string' && overriddenPhp.trim() !== '') {
+    process.stdout.write(overriddenPhp.trim());
+  }
+} catch (_) {}
+"
+}
+
+normalize_constraint_to_version() {
+  local php_constraint
+  php_constraint="$1"
+
+  if [[ "$php_constraint" =~ ([0-9]+)\.([0-9]+) ]]; then
+    local major
+    local minor
+    major="${BASH_REMATCH[1]}"
+    minor="${BASH_REMATCH[2]}"
+    echo "$((10#$major)).$((10#$minor))"
+  fi
+}
+
+DEFAULT_VERSION=$(get_default_version "$ENGINE") || exit 1
+DETECTED_CONSTRAINT=$(get_constraint_from_composer_json)
+
+if [ -z "$DETECTED_CONSTRAINT" ]; then
+  DETECTED_CONSTRAINT=$(get_constraint_from_composer_lock)
+fi
+
+if [ -n "$DETECTED_CONSTRAINT" ]; then
+  DETECTED_VERSION=$(normalize_constraint_to_version "$DETECTED_CONSTRAINT")
+fi
+
+if [ -n "$DETECTED_VERSION" ]; then
+  echo "$DETECTED_VERSION"
+else
+  echo "$DEFAULT_VERSION"
+fi
diff --git a/bin/setup.sh b/bin/setup.sh
index a24f4623..b5b31a5e 100644
--- a/bin/setup.sh
+++ b/bin/setup.sh
@@ -8,23 +8,15 @@ NEW_WIKI_CHECKOUT_PATH="${RUNNER_TEMP}/new-wiki-${ACTION_SUFFIX}"
 TMP_BRANCH_MAP_FILE="${RUNNER_TEMP}/branches-map-${ACTION_SUFFIX}"
 ACTION_BIN_PATH="${GITHUB_ACTION_PATH}/bin"
 
-if [ "$ENGINE" == "evert/phpdoc-md" ]; then
-  NEEDED_PHP_VERSION=7.4
-elif [ "$ENGINE" == "clean/phpdoc-md" ]; then
-  NEEDED_PHP_VERSION=8.1
-else
-  echo 'ERROR: unknown engine'
+NEEDED_PHP_VERSION=$(bash "$ACTION_BIN_PATH/resolve-php-version.sh" "$ENGINE") || exit 1
 
-  exit 1
-fi;
-
-echo "OLD_WIKI_CHECKOUT_PATH=$OLD_WIKI_CHECKOUT_PATH" >> $GITHUB_ENV
-echo "NEW_WIKI_CHECKOUT_PATH=$NEW_WIKI_CHECKOUT_PATH" >> $GITHUB_ENV
-echo "NEEDED_PHP_VERSION=$NEEDED_PHP_VERSION" >> $GITHUB_ENV
-echo "ACTION_BIN_PATH=$ACTION_BIN_PATH" >> $GITHUB_ENV
-echo "TMP_BRANCH_MAP_FILE=$TMP_BRANCH_MAP_FILE" >> $GITHUB_ENV
+echo "OLD_WIKI_CHECKOUT_PATH=$OLD_WIKI_CHECKOUT_PATH" >> "$GITHUB_ENV"
+echo "NEW_WIKI_CHECKOUT_PATH=$NEW_WIKI_CHECKOUT_PATH" >> "$GITHUB_ENV"
+echo "NEEDED_PHP_VERSION=$NEEDED_PHP_VERSION" >> "$GITHUB_ENV"
+echo "ACTION_BIN_PATH=$ACTION_BIN_PATH" >> "$GITHUB_ENV"
+echo "TMP_BRANCH_MAP_FILE=$TMP_BRANCH_MAP_FILE" >> "$GITHUB_ENV"
 
 rm -rf "$OLD_WIKI_CHECKOUT_PATH" || true
 rm -rf "$NEW_WIKI_CHECKOUT_PATH" || true
 
-mkdir -p "$NEW_WIKI_CHECKOUT_PATH"
\ No newline at end of file
+mkdir -p "$NEW_WIKI_CHECKOUT_PATH"