diff --git a/scripts/byok-syntax-check.sh b/scripts/byok-syntax-check.sh
new file mode 100644
index 0000000000..4a3979ab05
--- /dev/null
+++ b/scripts/byok-syntax-check.sh
@@ -0,0 +1,86 @@
+#!/bin/bash
+# T03: Syntax validation on all BYOK-related modules
+set -e
+
+echo "=== MAIN PROCESS (must pass cleanly) ==="
+main_pass=0
+main_fail=0
+
+MAIN_FILES=(
+  "newIDE/electron-app/app/byok/errors.js"
+  "newIDE/electron-app/app/byok/buildSystemPrompt.js"
+  "newIDE/electron-app/app/byok/byokConfig.js"
+  "newIDE/electron-app/app/byok/requestStore.js"
+  "newIDE/electron-app/app/byok/callLLM.js"
+  "newIDE/electron-app/app/byok/byokMain.js"
+  "newIDE/electron-app/app/preload.js"
+)
+
+for f in "${MAIN_FILES[@]}"; do
+  out=$(node --check "$f" 2>&1)
+  rc=$?
+  if [ $rc -eq 0 ]; then
+    echo "PASS main: $f"
+    main_pass=$((main_pass+1))
+  else
+    echo "FAIL main: $f (rc=$rc)"
+    echo "  $out"
+    main_fail=$((main_fail+1))
+  fi
+done
+
+echo ""
+echo "=== RENDERER (Flow annotations expected — note genuine errors) ==="
+ren_pass=0
+ren_flow=0
+ren_fail=0
+
+RENDERER_FILES=(
+  "newIDE/app/src/Utils/GDevelopServices/ByokRouting.js"
+  "newIDE/app/src/Utils/GDevelopServices/Generation.js"
+  "newIDE/app/src/Utils/GDevelopServices/Usage.js"
+  "newIDE/app/src/AiGeneration/AiRequestChat/ByokConfigPanel.js"
+  "newIDE/app/src/AiGeneration/AiRequestChat/index.js"
+)
+
+for f in "${RENDERER_FILES[@]}"; do
+  out=$(node --check "$f" 2>&1)
+  rc=$?
+  if [ $rc -eq 0 ]; then
+    echo "PASS renderer: $f"
+    ren_pass=$((ren_pass+1))
+  else
+    # Classify: Flow-only vs genuine error
+    is_flow_only=true
+    while IFS= read -r line; do
+      if echo "$line" | grep -q "SyntaxError"; then
+        # Known Flow patterns
+        if echo "$line" | grep -qE "Missing initializer in const|Unexpected token.*typeof|Unexpected token ':'|Unexpected token '\('" ; then
+          :
+        else
+          is_flow_only=false
+        fi
+      fi
+    done <<< "$out"
+
+    if [ "$is_flow_only" = true ]; then
+      echo "FLOW renderer: $f (Flow annotations only — acceptable)"
+      ren_flow=$((ren_flow+1))
+    else
+      echo "FAIL renderer: $f (genuine syntax error)"
+      echo "$out" | head -10
+      ren_fail=$((ren_fail+1))
+    fi
+  fi
+done
+
+echo ""
+echo "=== SUMMARY ==="
+echo "Main:   $main_pass passed, $main_fail failed (of 7)"
+echo "Render: $ren_pass clean, $ren_flow flow-only, $ren_fail genuine errors (of 5)"
+echo "Total files: 12"
+
+if [ $main_fail -gt 0 ] || [ $ren_fail -gt 0 ]; then
+  exit 1
+fi
+exit 0