diff --git a/scripts/frontend-test-coverage.sh b/scripts/frontend-test-coverage.sh
index 3444605d..434bbb39 100755
--- a/scripts/frontend-test-coverage.sh
+++ b/scripts/frontend-test-coverage.sh
@@ -37,25 +37,68 @@ fi
 # Extract and print total coverage summary using python
 LINES_PERCENT=$(python3 - <<'PY'
 import json
-summary = json.load(open('coverage/coverage-summary.json'))['total']
+import sys
+
+try:
+    with open('coverage/coverage-summary.json') as f:
+        summary = json.load(f)
+except json.JSONDecodeError as e:
+    print(f"Error: Invalid JSON in coverage-summary.json: {e}", file=sys.stderr)
+    sys.exit(1)
+except KeyError as e:
+    print(f"Error: Missing key in coverage-summary.json: {e}", file=sys.stderr)
+    sys.exit(1)
+
+# Validate structure
+if 'total' not in summary:
+    print("Error: 'total' key not found in coverage-summary.json", file=sys.stderr)
+    sys.exit(1)
+
+total = summary['total']
+metrics = ['statements', 'branches', 'functions', 'lines']
+for metric in metrics:
+    if metric not in total:
+        print(f"Error: '{metric}' metric missing from coverage summary", file=sys.stderr)
+        sys.exit(1)
+    if not isinstance(total[metric], dict) or 'pct' not in total[metric]:
+        print(f"Error: '{metric}' metric missing 'pct' field", file=sys.stderr)
+        sys.exit(1)
+
 def fmt(metric):
     return f"{metric['pct']}% ({metric['covered']}/{metric['total']})"
 
 print("Frontend coverage summary:")
-print(f"  Statements: {fmt(summary['statements'])}")
-print(f"  Branches:   {fmt(summary['branches'])}")
-print(f"  Functions:  {fmt(summary['functions'])}")
-print(f"  Lines:      {fmt(summary['lines'])}")
+print(f"  Statements: {fmt(total['statements'])}")
+print(f"  Branches:   {fmt(total['branches'])}")
+print(f"  Functions:  {fmt(total['functions'])}")
+print(f"  Lines:      {fmt(total['lines'])}")
 
-print(summary['lines']['pct'])
+lines_pct = total['lines']['pct']
+
+# Validate that lines pct is numeric
+if not isinstance(lines_pct, (int, float)):
+    print(f"Error: Coverage percentage is not numeric: {lines_pct} ({type(lines_pct).__name__})", file=sys.stderr)
+    sys.exit(1)
+
+# Print just the numeric value
+print(lines_pct)
 PY
 )
 
 python3 - <<PY
 import sys
-from decimal import Decimal
+from decimal import Decimal, InvalidOperation
+
+if not '$LINES_PERCENT':
+    print("Error: Failed to extract coverage percentage from test output", file=sys.stderr)
+    sys.exit(1)
+
+try:
+    total = Decimal('$LINES_PERCENT')
+except InvalidOperation as e:
+    print(f"Error: Coverage value is not numeric: '$LINES_PERCENT' ({e})", file=sys.stderr)
+    sys.exit(1)
 
-total = Decimal('$LINES_PERCENT')
 minimum = Decimal('$MIN_COVERAGE')
 status = "PASS" if total >= minimum else "FAIL"
 print(f"Coverage gate: {status} (lines {total}% vs minimum {minimum}%)")
diff --git a/scripts/go-test-coverage.sh b/scripts/go-test-coverage.sh
index de93b6fb..f9f72bbb 100755
--- a/scripts/go-test-coverage.sh
+++ b/scripts/go-test-coverage.sh
@@ -101,10 +101,46 @@ COVERAGE_OUTPUT=$(timeout 180 go tool cover -func="$COVERAGE_FILE" 2>&1) || {
 
 # Extract and display the summary line (total coverage)
 TOTAL_LINE=$(echo "$COVERAGE_OUTPUT" | awk '/^total:/ {line=$0} END {print line}')
+
+if [ -z "$TOTAL_LINE" ]; then
+    echo "Error: Coverage report missing 'total:' line"
+    echo "Coverage output:"
+    echo "$COVERAGE_OUTPUT"
+    exit 1
+fi
+
 echo "$TOTAL_LINE"
 
-# Extract total coverage percentage
-TOTAL_PERCENT=$(echo "$TOTAL_LINE" | awk '{print substr($3, 1, length($3)-1)}')
+# Extract total coverage percentage (format: "total: (statements)% (branches)% (functions)% (lines)% XX.X%")
+# Field $3 is the third space-separated token (line count %)
+# We need to remove trailing '%' character
+TOTAL_PERCENT=$(echo "$TOTAL_LINE" | awk '{
+    if (NF < 3) {
+        print "ERROR: Invalid coverage line format" > "/dev/stderr"
+        exit 1
+    }
+    # Extract last field and remove trailing %
+    last_field = $NF
+    if (last_field !~ /^[0-9]+(\.[0-9]+)?%$/) {
+        printf "ERROR: Last field is not a valid percentage: %s\n", last_field > "/dev/stderr"
+        exit 1
+    }
+    # Remove trailing %
+    gsub(/%$/, "", last_field)
+    print last_field
+}')
+
+if [ -z "$TOTAL_PERCENT" ] || [ "$TOTAL_PERCENT" = "ERROR" ]; then
+    echo "Error: Could not extract coverage percentage from: $TOTAL_LINE"
+    exit 1
+fi
+
+# Validate that extracted value is numeric (allows decimals and integers)
+if ! echo "$TOTAL_PERCENT" | grep -qE '^[0-9]+(\.[0-9]+)?$'; then
+    echo "Error: Extracted coverage value is not numeric: '$TOTAL_PERCENT'"
+    echo "Source line: $TOTAL_LINE"
+    exit 1
+fi
 
 echo "Computed coverage: ${TOTAL_PERCENT}% (minimum required ${MIN_COVERAGE}%)"
 
@@ -112,11 +148,28 @@ export TOTAL_PERCENT
 export MIN_COVERAGE
 
 python3 - <<'PY'
-import os, sys
-from decimal import Decimal
+import os
+import sys
+from decimal import Decimal, InvalidOperation
+
+try:
+    total = Decimal(os.environ['TOTAL_PERCENT'])
+except InvalidOperation as e:
+    print(f"Error: TOTAL_PERCENT is not numeric: '{os.environ['TOTAL_PERCENT']}' ({e})", file=sys.stderr)
+    sys.exit(1)
+except KeyError:
+    print("Error: TOTAL_PERCENT environment variable not set", file=sys.stderr)
+    sys.exit(1)
+
+try:
+    minimum = Decimal(os.environ['MIN_COVERAGE'])
+except InvalidOperation as e:
+    print(f"Error: MIN_COVERAGE is not numeric: '{os.environ['MIN_COVERAGE']}' ({e})", file=sys.stderr)
+    sys.exit(1)
+except KeyError:
+    print("Error: MIN_COVERAGE environment variable not set", file=sys.stderr)
+    sys.exit(1)
 
-total = Decimal(os.environ['TOTAL_PERCENT'])
-minimum = Decimal(os.environ['MIN_COVERAGE'])
 if total < minimum:
     print(f"Coverage {total}% is below required {minimum}% (set CHARON_MIN_COVERAGE or CPM_MIN_COVERAGE to override)", file=sys.stderr)
     sys.exit(1)