diff --git a/scripts/preflight.sh b/scripts/preflight.sh
index d356897..f868cc6 100755
--- a/scripts/preflight.sh
+++ b/scripts/preflight.sh
@@ -123,7 +123,60 @@ elif [ -f yarn.lock ] && command -v yarn >/dev/null 2>&1; then
   fi
 fi
 
-# 3) Check PR size locally (against BASE)
+# 3) CHANGELOG validation (for non-docs branches)
+# Branch prefixes that are exempt from CHANGELOG updates (configuration)
+CHANGELOG_EXEMPT_PREFIXES="^(docs|chore|ci|test)/"
+# Minimum lines in [Unreleased] to consider it non-empty
+# This counts substantive content lines (not headings, blanks, or HTML comments)
+# Minimum 3 ensures at least some documentation (e.g., 1-2 bullet points)
+MIN_CHANGELOG_LINES=3
+
+# Helper function to filter CHANGELOG content (POSIX-compliant with whitespace tolerance)
+filter_changelog_content() {
+  grep -Ev '^##' | grep -Ev '^$' | grep -Ev '^[[:space:]]*<!--' | grep -Ev '^[[:space:]]*-->'
+}
+
+CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD 2>/dev/null || echo "")
+# Use POSIX-compliant case statement instead of bash-specific [[ =~ ]] for portability
+BRANCH_IS_EXEMPT=false
+case "$CURRENT_BRANCH" in
+  docs/*|chore/*|ci/*|test/*)
+    BRANCH_IS_EXEMPT=true
+    ;;
+esac
+
+if [ -f CHANGELOG.md ] && [ "$CURRENT_BRANCH" != "main" ] && [ "$BRANCH_IS_EXEMPT" = false ]; then
+  # Check if CHANGELOG has [Unreleased] section
+  if ! grep -q "## \[Unreleased\]" CHANGELOG.md; then
+    echo "❌ CHANGELOG.md missing [Unreleased] section" >&2
+    echo "Tip: Every feature/fix/refactor branch must update CHANGELOG.md" >&2
+    echo "Exempt branches: docs/*, chore/*, ci/*, test/*" >&2
+    exit 1
+  fi
+
+  # Check if there's actual content after [Unreleased] (robust to last/only section)
+  # Find line number of [Unreleased], then extract content up to next heading or EOF
+  # Use grep -nE for robustness with Keep a Changelog format (supports links)
+  UNRELEASED_START=$(grep -nE '^## \[Unreleased\]' CHANGELOG.md | cut -d: -f1)
+  if [ -n "$UNRELEASED_START" ]; then
+    # Find next heading after [Unreleased], or use EOF if none found
+    UNRELEASED_END=$(tail -n +"$((UNRELEASED_START + 1))" CHANGELOG.md | grep -n '^## ' | head -1 | cut -d: -f1)
+    if [ -n "$UNRELEASED_END" ]; then
+      # Extract content between [Unreleased] and next heading (using helper function)
+      UNRELEASED_CONTENT=$(sed -n "$((UNRELEASED_START + 1)),$((UNRELEASED_START + UNRELEASED_END - 1))p" CHANGELOG.md | filter_changelog_content | wc -l)
+    else
+      # [Unreleased] is the last section, extract all remaining content (using helper function)
+      UNRELEASED_CONTENT=$(tail -n +"$((UNRELEASED_START + 1))" CHANGELOG.md | filter_changelog_content | wc -l)
+    fi
+
+    if [ "$UNRELEASED_CONTENT" -lt "$MIN_CHANGELOG_LINES" ]; then
+      echo "⚠️  Warning: [Unreleased] section appears empty in CHANGELOG.md" >&2
+      echo "Did you forget to document your changes?" >&2
+    fi
+  fi
+fi
+
+# 4) Check PR size locally (against BASE)
 if ! git rev-parse -q --verify "origin/$BASE" >/dev/null 2>&1; then
   echo "Warning: Cannot verify base branch origin/$BASE - skipping PR size check." >&2
   echo "Tip: Run 'git fetch origin $BASE' to enable PR size checking." >&2