diff --git a/chrome/browser/ai/ai_language_model.cc b/chrome/browser/ai/ai_language_model.cc
index a35583d2e4e2d..9a715f6bf9649 100644
--- a/chrome/browser/ai/ai_language_model.cc
+++ b/chrome/browser/ai/ai_language_model.cc
@@ -159,6 +159,9 @@ on_device_model::mojom::InputPtr ConvertToInput(
           // TODO(crbug.com/422803232): Support on_device_model tool use.
           return nullptr;
         case blink::mojom::AILanguageModelPromptContent::Tag::kToolResponse: {
+          if (!capabilities.Has(on_device_model::CapabilityFlags::kToolUse)) {
+            return nullptr;
+          }
           // TODO(crbug.com/422803232): Support image/audio result types.
           auto response = GetToolResponseFromDict(content->get_tool_response());
           if (!response) {
diff --git a/chrome/browser/ai/ai_manager.cc b/chrome/browser/ai/ai_manager.cc
index 440c485e903ca..32744a016e259 100644
--- a/chrome/browser/ai/ai_manager.cc
+++ b/chrome/browser/ai/ai_manager.cc
@@ -688,9 +688,15 @@ void AIManager::CanCreateLanguageModel(
                                   kUnavailableModelAdaptationNotAvailable);
       return;
     }
-    // Note: Tool use capabilities are gated by RuntimeEnabledFeatures in Blink.
     // Tool use capability is signaled by the presence of tool declarations.
     if (options->tools.has_value() && !options->tools->empty()) {
+      // Browser-side re-validation of the renderer-only RuntimeEnabledFeatures
+      // gate; do not trust the renderer to have enforced it.
+      if (!base::FeatureList::IsEnabled(blink::features::kAIPromptAPIToolUse)) {
+        std::move(callback).Run(blink::mojom::ModelAvailabilityCheckResult::
+                                    kUnavailableModelAdaptationNotAvailable);
+        return;
+      }
       input_capabilities.Put(on_device_model::CapabilityFlags::kToolUse);
     }
   }
@@ -846,11 +852,16 @@ void AIManager::CreateLanguageModelInternal(
     return;
   }
   if (!params->capabilities.empty()) {
-    // Check if multimodal input (image/audio) is used without the feature flag
-    // or if the model doesn't support the requested capabilities.
+    // Check if multimodal input (image/audio) is used without the feature flag,
+    // tool use is requested without the feature flag, or the model doesn't
+    // support the requested capabilities. Do not trust the renderer to have
+    // enforced the matching RuntimeEnabledFeatures gates.
     if ((HasMultimodalInputCapabilities(params->capabilities) &&
          !base::FeatureList::IsEnabled(
              blink::features::kAIPromptAPIMultimodalInput)) ||
+        (params->capabilities.Has(on_device_model::CapabilityFlags::kToolUse) &&
+         !base::FeatureList::IsEnabled(
+             blink::features::kAIPromptAPIToolUse)) ||
         !model_client->capabilities().HasAll(params->capabilities)) {
       mojo::Remote<blink::mojom::AIManagerCreateLanguageModelClient>
           client_remote(std::move(client));