diff --git a/ralph.sh b/ralph.sh
index baff052a..ea29c353 100755
--- a/ralph.sh
+++ b/ralph.sh
@@ -39,32 +39,40 @@ PROGRESS_FILE="$SCRIPT_DIR/progress.txt"
 ARCHIVE_DIR="$SCRIPT_DIR/archive"
 LAST_BRANCH_FILE="$SCRIPT_DIR/.last-branch"
 
+# ------------------------------------------------------------
+# Fail fast on malformed PRDs before starting the agent loop
+# ------------------------------------------------------------
+if [ -f "$SCRIPT_DIR/scripts/validate_prd.sh" ]; then
+  "$SCRIPT_DIR/scripts/validate_prd.sh" "$PRD_FILE"
+fi
+
+# ------------------------------------------------------------
 # Archive previous run if branch changed
+# ------------------------------------------------------------
 if [ -f "$PRD_FILE" ] && [ -f "$LAST_BRANCH_FILE" ]; then
   CURRENT_BRANCH=$(jq -r '.branchName // empty' "$PRD_FILE" 2>/dev/null || echo "")
   LAST_BRANCH=$(cat "$LAST_BRANCH_FILE" 2>/dev/null || echo "")
-  
+
   if [ -n "$CURRENT_BRANCH" ] && [ -n "$LAST_BRANCH" ] && [ "$CURRENT_BRANCH" != "$LAST_BRANCH" ]; then
-    # Archive the previous run
     DATE=$(date +%Y-%m-%d)
-    # Strip "ralph/" prefix from branch name for folder
     FOLDER_NAME=$(echo "$LAST_BRANCH" | sed 's|^ralph/||')
     ARCHIVE_FOLDER="$ARCHIVE_DIR/$DATE-$FOLDER_NAME"
-    
+
     echo "Archiving previous run: $LAST_BRANCH"
     mkdir -p "$ARCHIVE_FOLDER"
     [ -f "$PRD_FILE" ] && cp "$PRD_FILE" "$ARCHIVE_FOLDER/"
     [ -f "$PROGRESS_FILE" ] && cp "$PROGRESS_FILE" "$ARCHIVE_FOLDER/"
     echo "   Archived to: $ARCHIVE_FOLDER"
-    
-    # Reset progress file for new run
+
     echo "# Ralph Progress Log" > "$PROGRESS_FILE"
     echo "Started: $(date)" >> "$PROGRESS_FILE"
     echo "---" >> "$PROGRESS_FILE"
   fi
 fi
 
+# ------------------------------------------------------------
 # Track current branch
+# ------------------------------------------------------------
 if [ -f "$PRD_FILE" ]; then
   CURRENT_BRANCH=$(jq -r '.branchName // empty' "$PRD_FILE" 2>/dev/null || echo "")
   if [ -n "$CURRENT_BRANCH" ]; then
@@ -72,7 +80,9 @@ if [ -f "$PRD_FILE" ]; then
   fi
 fi
 
-# Initialize progress file if it doesn't exist
+# ------------------------------------------------------------
+# Initialize progress file if needed
+# ------------------------------------------------------------
 if [ ! -f "$PROGRESS_FILE" ]; then
   echo "# Ralph Progress Log" > "$PROGRESS_FILE"
   echo "Started: $(date)" >> "$PROGRESS_FILE"
@@ -81,8 +91,12 @@ fi
 
 echo "Starting Ralph - Tool: $TOOL - Max iterations: $MAX_ITERATIONS"
 
-for i in $(seq 1 $MAX_ITERATIONS); do
+# ------------------------------------------------------------
+# Main agent loop
+# ------------------------------------------------------------
+for i in $(seq 1 "$MAX_ITERATIONS"); do
   echo ""
+
   echo "==============================================================="
   echo "  Ralph Iteration $i of $MAX_ITERATIONS ($TOOL)"
   echo "==============================================================="
@@ -102,7 +116,7 @@ for i in $(seq 1 $MAX_ITERATIONS); do
     echo "Completed at iteration $i of $MAX_ITERATIONS"
     exit 0
   fi
-  
+
   echo "Iteration $i complete. Continuing..."
   sleep 2
 done
diff --git a/scripts/validate_prd.sh b/scripts/validate_prd.sh
new file mode 100644
index 00000000..517d4648
--- /dev/null
+++ b/scripts/validate_prd.sh
@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+set -e
+
+FILE=${1:-prd.json}
+
+# Ensure PRD file exists
+if [ ! -f "$FILE" ]; then
+  echo "✗ PRD file not found: $FILE"
+  exit 1
+fi
+
+# Ensure jq is available
+if ! command -v jq >/dev/null 2>&1; then
+  echo "✗ jq is required but not installed"
+  exit 1
+fi
+
+# Fields that must exist on each user story
+REQUIRED_FIELDS=("id" "title" "priority")
+ERROR=0
+
+echo "Validating PRD: $FILE"
+echo "-------------------------"
+
+# Ensure userStories exists and is an array
+if ! jq -e '.userStories | type == "array"' "$FILE" >/dev/null; then
+  echo "✗ 'userStories' must be an array"
+  exit 1
+fi
+
+# Check for duplicate IDs
+IDS=$(jq -r '.userStories[].id' "$FILE")
+DUP_IDS=$(echo "$IDS" | sort | uniq -d)
+if [ -n "$DUP_IDS" ]; then
+  echo "✗ Duplicate userStory IDs:"
+  echo "$DUP_IDS"
+  ERROR=1
+fi
+
+# Validate required fields exist (existence, not truthiness)
+COUNT=$(jq '.userStories | length' "$FILE")
+for ((i=0; i<COUNT; i++)); do
+  for FIELD in "${REQUIRED_FIELDS[@]}"; do
+    EXISTS=$(jq ".userStories[$i] | has(\"$FIELD\")" "$FILE")
+    if [ "$EXISTS" != "true" ]; then
+      echo "✗ Missing field '$FIELD' in userStory index $i"
+      ERROR=1
+    fi
+  done
+done
+
+if [ "$ERROR" -eq 0 ]; then
+  echo "✓ PRD is valid"
+else
+  echo "✗ PRD validation failed"
+  exit 1
+fi