Fix app tool routing: visibility check and middleware propagation (#3591)

src/fastmcp/server/app.py

@@ -354,9 +354,12 @@ class FastMCPApp(Provider):
         if not isinstance(tool, Tool):
             tool = Tool._ensure_tool(tool)
 
-        # Tag with app name for routing
+        # Tag with app name and visibility for routing
         meta = dict(tool.meta) if tool.meta else {}
         meta.setdefault("fastmcp", {})["app"] = self.name
+        ui = meta.setdefault("ui", {})
+        if "visibility" not in ui:
+            ui["visibility"] = ["app"]
         tool.meta = meta
 
         self._local._add_component(tool)

src/fastmcp/server/providers/base.py

@@ -194,7 +194,16 @@ class Provider:
         if tool is not None:
             meta = tool.meta or {}
             fastmcp_meta = meta.get("fastmcp")
-            if isinstance(fastmcp_meta, dict) and fastmcp_meta.get("app") == app_name:
+            ui_meta = meta.get("ui")
+            # Must match app name AND have app visibility (not model-only)
+            visibility = (
+                ui_meta.get("visibility", []) if isinstance(ui_meta, dict) else []
+            )
+            if (
+                isinstance(fastmcp_meta, dict)
+                and fastmcp_meta.get("app") == app_name
+                and "app" in visibility
+            ):
                 return tool
         return None
 

src/fastmcp/server/providers/fastmcp_provider.py

@@ -137,11 +137,23 @@ class FastMCPProviderTool(Tool):
         # Pass exact version so child executes the correct version
         version = VersionSpec(eq=self.version) if self.version else None
 
+        # If this tool belongs to a FastMCPApp, pass app_name so the
+        # child server routes via get_app_tool (bypassing transforms).
+        app_name: str | None = None
+        meta = self.meta or {}
+        fastmcp_meta = meta.get("fastmcp")
+        if isinstance(fastmcp_meta, dict):
+            app_name = fastmcp_meta.get("app")
+
         with delegate_span(
             self._original_name or "", "FastMCPProvider", self._original_name or ""
         ):
             return await self._server.call_tool(
-                self._original_name, arguments, version=version, task_meta=task_meta
+                self._original_name,
+                arguments,
+                version=version,
+                task_meta=task_meta,
+                app_name=app_name,
             )
 
     async def run(self, arguments: dict[str, Any]) -> ToolResult:
@@ -153,8 +165,14 @@ class FastMCPProviderTool(Tool):
         # Pass exact version so child executes the correct version
         version = VersionSpec(eq=self.version) if self.version else None
 
+        app_name: str | None = None
+        meta = self.meta or {}
+        fastmcp_meta = meta.get("fastmcp")
+        if isinstance(fastmcp_meta, dict):
+            app_name = fastmcp_meta.get("app")
+
         result = await self._server.call_tool(
-            self._original_name, arguments, version=version
+            self._original_name, arguments, version=version, app_name=app_name
         )
         # Result from call_tool should always be ToolResult when no task_meta
         if isinstance(result, mcp.types.CreateTaskResult):
@@ -563,8 +581,11 @@ class FastMCPProvider(Provider):
         return FastMCPProviderTool.wrap(self.server, raw_tool)
 
     async def get_app_tool(self, app_name: str, tool_name: str) -> Tool | None:
-        """Delegate to nested server's get_app_tool, bypassing transforms."""
-        return await self.server.get_app_tool(app_name, tool_name)
+        """Delegate to nested server's get_app_tool, wrapping for middleware."""
+        raw_tool = await self.server.get_app_tool(app_name, tool_name)
+        if raw_tool is None:
+            return None
+        return FastMCPProviderTool.wrap(self.server, raw_tool)
 
     # -------------------------------------------------------------------------
     # Resource methods

tests/test_fastmcp_app.py

@@ -386,8 +386,9 @@ class TestGetAppTool:
         assert tool is not None
         assert tool.name == "save_contact"
 
-    async def test_ui_tool_findable_by_app_name(self):
-        """@app.ui() tools are also tagged with app name."""
+    async def test_ui_tool_not_findable_via_get_app_tool(self):
+        """@app.ui() tools have model visibility and should NOT be
+        returned by get_app_tool (only app-visible tools are)."""
         app = FastMCPApp("dashboard")
 
         @app.ui()
@@ -395,6 +396,17 @@ class TestGetAppTool:
             return "ui"
 
         tool = await app.get_app_tool("dashboard", "show")
+        assert tool is None
+
+    async def test_model_visible_tool_findable(self):
+        """@app.tool(model=True) has app visibility and IS findable."""
+        app = FastMCPApp("test")
+
+        @app.tool(model=True)
+        def query(q: str) -> str:
+            return q
+
+        tool = await app.get_app_tool("test", "query")
         assert tool is not None