diff --git a/onnxruntime/core/providers/webnn/builders/helper.h b/onnxruntime/core/providers/webnn/builders/helper.h
index 92aa9abc9fdf7..d94729e60d029 100644
--- a/onnxruntime/core/providers/webnn/builders/helper.h
+++ b/onnxruntime/core/providers/webnn/builders/helper.h
@@ -54,6 +54,10 @@ std::string GetShapeString(std::vector<T>& shape) {
   return shape_info.str();
 }
 
+inline std::string GetTensorName(const ConstPointerContainer<std::vector<NodeArg*>>& input_defs, const size_t index) {
+  return (input_defs.size() > index) ? std::string(input_defs[index]->Name()) : "";
+}
+
 inline std::vector<uint32_t> GetVecUint32FromVecInt64(const std::vector<int64_t>& int64_vec) {
   std::vector<uint32_t> uint32_vec;
   uint32_vec.reserve(int64_vec.size());
diff --git a/onnxruntime/core/providers/webnn/builders/impl/pad_op_builder.cc b/onnxruntime/core/providers/webnn/builders/impl/pad_op_builder.cc
index a2a1e2f2e599d..52b5518857773 100644
--- a/onnxruntime/core/providers/webnn/builders/impl/pad_op_builder.cc
+++ b/onnxruntime/core/providers/webnn/builders/impl/pad_op_builder.cc
@@ -178,8 +178,10 @@ bool PadOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& initializers,
       return false;
     }
     for (size_t i = 1; i < input_defs.size(); i++) {
-      if (!Contains(initializers, input_defs[i]->Name())) {
-        LOGS(logger, VERBOSE) << "Input [" << input_defs[i]->Name() << "] must be known as initializer";
+      // Optional tensors (constant_value, axes) can be indicated by an empty name, just ignore it.
+      const std::string input_name = GetTensorName(input_defs, i);
+      if (!input_name.empty() && !Contains(initializers, input_name)) {
+        LOGS(logger, VERBOSE) << "Input [" << input_name << "] must be known as initializer";
         return false;
       }
     }
diff --git a/onnxruntime/core/providers/webnn/builders/impl/reduction_op_builder.cc b/onnxruntime/core/providers/webnn/builders/impl/reduction_op_builder.cc
index 1a702649b7f05..f446a7b81d1c0 100644
--- a/onnxruntime/core/providers/webnn/builders/impl/reduction_op_builder.cc
+++ b/onnxruntime/core/providers/webnn/builders/impl/reduction_op_builder.cc
@@ -134,8 +134,9 @@ bool ReductionOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& initializ
     return false;
 
   const auto& op_type = node.OpType();
+  const std::string axes_name = GetTensorName(input_defs, 1);
   // If the optional input 'axes' is provided, it must be an initializer.
-  if (input_defs.size() > 1 && !Contains(initializers, input_defs[1]->Name())) {
+  if (!axes_name.empty() && !Contains(initializers, axes_name)) {
     LOGS(logger, VERBOSE) << "Input axes of " << op_type << " must be a constant";
     return false;
   }
diff --git a/onnxruntime/core/providers/webnn/builders/impl/resize_op_builder.cc b/onnxruntime/core/providers/webnn/builders/impl/resize_op_builder.cc
index 186d1e7c1035a..9018f8c96f300 100644
--- a/onnxruntime/core/providers/webnn/builders/impl/resize_op_builder.cc
+++ b/onnxruntime/core/providers/webnn/builders/impl/resize_op_builder.cc
@@ -120,8 +120,9 @@ Status ResizeOpBuilder::AddToModelBuilderImpl(ModelBuilder& model_builder,
   std::vector<float> scales_hw;
   std::vector<int32_t> sizes_hw;
   std::vector<int32_t> axes;
+  std::string scales_name = GetTensorName(input_defs, 2);
   const bool is_nhwc = model_builder.GetPreferredLayout() == DataLayout::NHWC;
-  if (input_defs.size() == 3) {  // Use scales.
+  if (!scales_name.empty()) {  // Use scales.
     ORT_RETURN_IF_NOT(GetResizeScales(initializers, node, scales, logger), "Error getting resize scales");
     if (is_nhwc) {
       scales_hw = {scales[1], scales[2]};
@@ -129,7 +130,7 @@ Status ResizeOpBuilder::AddToModelBuilderImpl(ModelBuilder& model_builder,
       scales_hw = {scales[2], scales[3]};
     }
     options.set("scales", emscripten::val::array(scales_hw));
-  } else {  // We already checked number of inputs in IsOpSupportedImpl.
+  } else {  // Use sizes, we already checked inputs in IsOpSupportedImpl.
     std::vector<int64_t> output_sizes;
     ORT_RETURN_IF_NOT(GetResizeOutputSizes(initializers, node, output_sizes, logger),
                       "Error getting resize output_sizes");
@@ -203,26 +204,31 @@ bool ResizeOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& initializers
   }
 
   {  // scales and sizes (if present) must be initializers.
-    if (input_defs.size() < 3) {
-      LOGS(logger, VERBOSE) << "Input scales or sizes of Resize must be known";
-      return false;
-    }
+    const std::string scales_name = GetTensorName(input_defs, 2);
+    const std::string sizes_name = GetTensorName(input_defs, 3);
 
-    // scales
-    if (input_defs.size() == 3 && !Contains(initializers, input_defs[2]->Name())) {
+    // scales (scales may be empty tensor)
+    bool has_scales = !scales_name.empty();
+    if ((has_scales && !Contains(initializers, scales_name)) || (!has_scales && node.SinceVersion() == 11)) {
       LOGS(logger, VERBOSE) << "Input scales of Resize must be known";
       return false;
     }
 
-    // sizes
-    if (input_defs.size() > 3 && !Contains(initializers, input_defs[3]->Name())) {
+    // sizes (sizes may be empty tensor)
+    bool has_sizes = !sizes_name.empty();
+    if (has_sizes && !Contains(initializers, sizes_name)) {
       LOGS(logger, VERBOSE) << "Input sizes of Resize must be known";
       return false;
     }
 
+    if (has_scales && has_sizes) {
+      LOGS(logger, VERBOSE) << "Only one of 'scales' and 'sizes' can be specified";
+      return false;
+    }
+
     const bool is_nhwc = node.Domain() == kMSInternalNHWCDomain;
     // We want to check if the scales or sizes are not trying to resize on N/C channels here.
-    if (input_defs.size() == 3) {  // We are using scales.
+    if (has_scales) {  // We are using scales.
       std::vector<float> scales;
       if (!GetResizeScales(initializers, node, scales, logger))
         return false;
@@ -251,7 +257,9 @@ bool ResizeOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& initializers
         LOGS(logger, VERBOSE) << "Resize: scale_w: " << scale_w << " is not a whole number";
         return false;
       }
-    } else {
+    }
+
+    if (has_sizes) {
       // We are using sizes.
       std::vector<int64_t> output_sizes;
       if (!GetResizeOutputSizes(initializers, node, output_sizes, logger))
diff --git a/onnxruntime/core/providers/webnn/builders/impl/slice_op_builder.cc b/onnxruntime/core/providers/webnn/builders/impl/slice_op_builder.cc
index e48cf35012652..4e0628581abf2 100644
--- a/onnxruntime/core/providers/webnn/builders/impl/slice_op_builder.cc
+++ b/onnxruntime/core/providers/webnn/builders/impl/slice_op_builder.cc
@@ -123,8 +123,10 @@ bool SliceOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& initializers,
 
   // Inputs: starts, ends, axes, and steps must be constant initializers if present.
   for (size_t i = 1; i < input_defs.size(); i++) {
-    if (!Contains(initializers, input_defs[i]->Name())) {
-      LOGS(logger, VERBOSE) << "Input [" << input_defs[i]->Name() << "] of " << op_type
+    // Optional tensors (axes, steps) can be indicated by an empty name, just ignore it.
+    const std::string input_name = GetTensorName(input_defs, i);
+    if (!input_name.empty() && !Contains(initializers, input_name)) {
+      LOGS(logger, VERBOSE) << "Input [" << input_name << "] of " << op_type
                             << " [" << name << "] must be known as initializer";
       return false;
     }
diff --git a/onnxruntime/core/providers/webnn/builders/impl/split_op_builder.cc b/onnxruntime/core/providers/webnn/builders/impl/split_op_builder.cc
index d568d4e625077..e9a600a5933af 100644
--- a/onnxruntime/core/providers/webnn/builders/impl/split_op_builder.cc
+++ b/onnxruntime/core/providers/webnn/builders/impl/split_op_builder.cc
@@ -136,9 +136,9 @@ bool SplitOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& initializers,
   int32_t axis = helper.Get("axis", 0);
   axis = SafeInt<int32_t>(HandleNegativeAxis(axis, rank));
 
-  if (input_defs.size() == 2) {
-    // Inputs contains optional 'split' input
-    const auto& split_name = input_defs[1]->Name();
+  const std::string split_name = GetTensorName(input_defs, 1);
+  // Inputs contain optional 'split' input.
+  if (!split_name.empty()) {
     if (!Contains(initializers, split_name)) {
       LOGS(logger, VERBOSE) << "The split must be a constant initializer.";
       return false;
@@ -166,7 +166,7 @@ bool SplitOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& initializers,
       LOGS(logger, VERBOSE) << "Sum of the split's values must be equal to the dim value at 'axis' specified.";
       return false;
     }
-  } else if (input_defs.size() == 1) {
+  } else {
     if (helper.HasAttr("num_outputs")) {
       // Split has 'num_outputs' attribute when opset is 18.
       const int32_t num_outputs = helper.Get("num_outputs", 1);
diff --git a/onnxruntime/core/providers/webnn/builders/impl/squeeze_unsqueeze_op_builder.cc b/onnxruntime/core/providers/webnn/builders/impl/squeeze_unsqueeze_op_builder.cc
index 2a1672c001b0e..9f6ccb98f79dd 100644
--- a/onnxruntime/core/providers/webnn/builders/impl/squeeze_unsqueeze_op_builder.cc
+++ b/onnxruntime/core/providers/webnn/builders/impl/squeeze_unsqueeze_op_builder.cc
@@ -138,8 +138,8 @@ bool SqueezeUnsqueezeOpBuilder::IsOpSupportedImpl(const InitializedTensorSet& in
 
   // Squeeze/Unsqueeze opset 13 uses input 1 as axes, it needs to be an initializer.
   if (node.SinceVersion() >= 13) {
-    if (input_defs.size() > 1) {
-      const auto& axes_name = input_defs[1]->Name();
+    const std::string axes_name = GetTensorName(input_defs, 1);
+    if (!axes_name.empty()) {
       if (!Contains(initializers, axes_name)) {
         LOGS(logger, ERROR) << "Input axes of " << op_type << " is not present and constant";
         return false;