diff --git a/server.py b/server.py
index 51e8c05..abc99e8 100644
--- a/server.py
+++ b/server.py
@@ -1652,22 +1652,28 @@ async def get_asset_by_name_legacy(name: str):
 
 @app.get("/assets/{name}")
 async def get_asset(name: str, request: Request):
-    """Get asset by name. HTML for browsers, JSON for APIs."""
+    """Get asset by name. HTML for browsers (default), JSON only if explicitly requested."""
     registry = await load_registry()
+
+    # Check if JSON explicitly requested
+    accept = request.headers.get("accept", "")
+    wants_json = "application/json" in accept and "text/html" not in accept
+
     if name not in registry.get("assets", {}):
-        if wants_html(request):
-            content = f'''
-            <h2 class="text-xl font-semibold text-white mb-4">Asset Not Found</h2>
-            <p class="text-gray-400">No asset named "{name}" exists.</p>
-            <p class="mt-4"><a href="/assets" class="text-blue-400 hover:text-blue-300">&larr; Back to Assets</a></p>
-            '''
-            return HTMLResponse(base_html("Asset Not Found", content, get_user_from_cookie(request)))
-        raise HTTPException(404, f"Asset not found: {name}")
+        if wants_json:
+            raise HTTPException(404, f"Asset not found: {name}")
+        content = f'''
+        <h2 class="text-xl font-semibold text-white mb-4">Asset Not Found</h2>
+        <p class="text-gray-400">No asset named "{name}" exists.</p>
+        <p class="mt-4"><a href="/assets" class="text-blue-400 hover:text-blue-300">&larr; Back to Assets</a></p>
+        '''
+        return HTMLResponse(base_html("Asset Not Found", content, get_user_from_cookie(request)))
 
-    if wants_html(request):
-        return await ui_asset_detail(name, request)
+    if wants_json:
+        return registry["assets"][name]
 
-    return registry["assets"][name]
+    # Default to HTML for browsers
+    return await ui_asset_detail(name, request)
 
 
 @app.get("/assets/by-run-id/{run_id}")
@@ -2372,26 +2378,30 @@ async def get_activities(request: Request, page: int = 1, limit: int = 20):
 
 @app.get("/activities/{activity_index}")
 async def get_activity_detail(activity_index: int, request: Request):
-    """Get single activity. HTML for browsers, JSON for APIs."""
+    """Get single activity. HTML for browsers (default), JSON only if explicitly requested."""
     activities = await load_activities()
 
+    # Check if JSON explicitly requested
+    accept = request.headers.get("accept", "")
+    wants_json = ("application/json" in accept or "application/activity+json" in accept) and "text/html" not in accept
+
     if activity_index < 0 or activity_index >= len(activities):
-        if wants_html(request):
-            content = '''
-            <h2 class="text-xl font-semibold text-white mb-4">Activity Not Found</h2>
-            <p class="text-gray-400">This activity does not exist.</p>
-            <p class="mt-4"><a href="/activities" class="text-blue-400 hover:text-blue-300">&larr; Back to Activities</a></p>
-            '''
-            return HTMLResponse(base_html("Activity Not Found", content, get_user_from_cookie(request)))
-        raise HTTPException(404, "Activity not found")
+        if wants_json:
+            raise HTTPException(404, "Activity not found")
+        content = '''
+        <h2 class="text-xl font-semibold text-white mb-4">Activity Not Found</h2>
+        <p class="text-gray-400">This activity does not exist.</p>
+        <p class="mt-4"><a href="/activities" class="text-blue-400 hover:text-blue-300">&larr; Back to Activities</a></p>
+        '''
+        return HTMLResponse(base_html("Activity Not Found", content, get_user_from_cookie(request)))
 
     activity = activities[activity_index]
 
-    if wants_html(request):
-        # Reuse the UI activity detail logic
-        return await ui_activity_detail(activity_index, request)
+    if wants_json:
+        return activity
 
-    return activity
+    # Default to HTML for browsers
+    return await ui_activity_detail(activity_index, request)
 
 
 @app.get("/activity/{activity_index}")
@@ -2408,12 +2418,12 @@ async def get_object(content_hash: str, request: Request):
     # Find asset by hash
     for name, asset in registry.get("assets", {}).items():
         if asset.get("content_hash") == content_hash:
-            # Check Accept header for content negotiation
+            # Check Accept header - only return JSON if explicitly requested
             accept = request.headers.get("accept", "")
-            wants_html = "text/html" in accept and "application/json" not in accept and "application/activity+json" not in accept
+            wants_json = ("application/json" in accept or "application/activity+json" in accept) and "text/html" not in accept
 
-            if wants_html:
-                # Redirect to detail page for browsers
+            if not wants_json:
+                # Default: redirect to detail page for browsers
                 return RedirectResponse(url=f"/assets/{name}", status_code=303)
 
             owner = asset.get("owner", "unknown")