diff --git a/frontend/src/__tests__/ConfigEditorAdvanced.test.tsx b/frontend/src/__tests__/ConfigEditorAdvanced.test.tsx
new file mode 100644
index 0000000..8a9ec24
--- /dev/null
+++ b/frontend/src/__tests__/ConfigEditorAdvanced.test.tsx
@@ -0,0 +1,210 @@
+/**
+ * TDD RED → GREEN: basic/advanced field filtering and profile section gate.
+ */
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, fireEvent, waitFor } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import type { ReactNode } from "react";
+
+vi.mock("@/lib/api", () => ({
+  apiClient: {
+    get: vi.fn(),
+    put: vi.fn(),
+    post: vi.fn(),
+    delete: vi.fn(),
+  },
+}));
+
+vi.mock("@/lib/logger", () => ({
+  logger: { error: vi.fn(), warn: vi.fn(), info: vi.fn(), debug: vi.fn() },
+}));
+
+import { apiClient } from "@/lib/api";
+import { ConfigEditor } from "@/components/servers/ConfigEditor";
+
+function createWrapper() {
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  return function Wrapper({ children }: { children: ReactNode }) {
+    return <QueryClientProvider client={qc}>{children}</QueryClientProvider>;
+  };
+}
+
+const BASIC_SERVER_SECTION = {
+  _meta: { config_version: "v1", schema_version: "1.1.0" },
+  hostname: "My Server",
+  max_players: 10,
+  kick_duplicate: 1,         // advanced
+  server_command_password: "",  // advanced
+  vote_threshold: 0.33,      // advanced
+};
+
+const SCHEMA_WITH_ADVANCED = {
+  server: {
+    hostname: { widget: "text", label: "Hostname", advanced: false },
+    max_players: { widget: "number", label: "Max Players", advanced: false },
+    kick_duplicate: { widget: "toggle", label: "Kick Duplicate", advanced: true },
+    server_command_password: { widget: "password", label: "SC Password", advanced: true },
+    vote_threshold: { widget: "number", label: "Vote Threshold", advanced: true },
+  },
+};
+
+const PROFILE_SECTION = {
+  _meta: { config_version: "v1", schema_version: "1.1.0" },
+  group_indicators: 1,
+  reduced_damage: 0,
+};
+
+const PROFILE_SCHEMA = {
+  profile: {
+    group_indicators: { widget: "toggle", label: "Group Indicators", advanced: false },
+    reduced_damage: { widget: "toggle", label: "Reduced Damage", advanced: true },
+  },
+};
+
+describe("ConfigEditor — basic/advanced filtering", () => {
+  beforeEach(() => {
+    vi.mocked(apiClient.get).mockReset();
+  });
+
+  function mockServerConfig(sections: Record<string, Record<string, unknown>>) {
+    const configMap: Record<string, unknown> = {};
+    for (const [k, v] of Object.entries(sections)) {
+      configMap[k] = v;
+    }
+    vi.mocked(apiClient.get).mockImplementation((url: string) => {
+      if (url.endsWith("/config/schema")) {
+        return Promise.resolve({ data: { success: true, data: { ...SCHEMA_WITH_ADVANCED } } });
+      }
+      if (url.endsWith("/config")) {
+        return Promise.resolve({ data: { success: true, data: configMap } });
+      }
+      if (url.includes("/config/")) {
+        const section = url.split("/config/")[1];
+        return Promise.resolve({ data: { success: true, data: sections[section] ?? {} } });
+      }
+      return Promise.resolve({ data: { success: true, data: {} } });
+    });
+  }
+
+  it("hides advanced fields by default", async () => {
+    mockServerConfig({ server: BASIC_SERVER_SECTION });
+    render(<ConfigEditor serverId={1} />, { wrapper: createWrapper() });
+
+    await screen.findByText("Hostname");
+    expect(screen.getByText("Hostname")).toBeInTheDocument();
+    expect(screen.queryByText("Kick Duplicate")).not.toBeInTheDocument();
+    expect(screen.queryByText("SC Password")).not.toBeInTheDocument();
+  });
+
+  it("shows advanced fields after clicking Show advanced", async () => {
+    mockServerConfig({ server: BASIC_SERVER_SECTION });
+    render(<ConfigEditor serverId={1} />, { wrapper: createWrapper() });
+
+    await screen.findByText("Hostname");
+    fireEvent.click(screen.getByText(/show advanced/i));
+
+    expect(screen.getByText("Kick Duplicate")).toBeInTheDocument();
+    expect(screen.getByText("SC Password")).toBeInTheDocument();
+  });
+
+  it("hides advanced fields again after toggling off", async () => {
+    mockServerConfig({ server: BASIC_SERVER_SECTION });
+    render(<ConfigEditor serverId={1} />, { wrapper: createWrapper() });
+
+    await screen.findByText("Hostname");
+    fireEvent.click(screen.getByText(/show advanced/i));
+    await screen.findByText("Kick Duplicate");
+    fireEvent.click(screen.getByText(/hide advanced/i));
+
+    await waitFor(() => {
+      expect(screen.queryByText("Kick Duplicate")).not.toBeInTheDocument();
+    });
+  });
+
+  it("shows all fields when no schema is available (graceful fallback)", async () => {
+    vi.mocked(apiClient.get).mockImplementation((url: string) => {
+      if (url.endsWith("/config")) {
+        return Promise.resolve({
+          data: { success: true, data: { server: BASIC_SERVER_SECTION } },
+        });
+      }
+      if (url.includes("/config/server")) {
+        return Promise.resolve({ data: { success: true, data: BASIC_SERVER_SECTION } });
+      }
+      if (url.endsWith("/config/schema")) {
+        return Promise.resolve({ data: { success: true, data: {} } }); // no schema
+      }
+      return Promise.resolve({ data: { success: true, data: {} } });
+    });
+
+    render(<ConfigEditor serverId={1} />, { wrapper: createWrapper() });
+    await screen.findByText("Hostname");
+    // Without schema, fields have no advanced flag — all should display
+    expect(screen.getByText("Hostname")).toBeInTheDocument();
+  });
+});
+
+describe("ConfigEditor — profile section gate", () => {
+  beforeEach(() => {
+    vi.mocked(apiClient.get).mockReset();
+  });
+
+  function mockWithDifficulty(difficulty: string) {
+    const serverSectionData = {
+      _meta: { config_version: "v1", schema_version: "1.1.0" },
+      forced_difficulty: difficulty,
+      hostname: "My Server",
+    };
+    vi.mocked(apiClient.get).mockImplementation((url: string) => {
+      if (url.endsWith("/config/schema")) {
+        return Promise.resolve({
+          data: {
+            success: true,
+            data: {
+              server: {
+                forced_difficulty: { widget: "select", label: "Difficulty", advanced: false, options: ["Recruit", "Regular", "Veteran", "Custom"] },
+                hostname: { widget: "text", label: "Hostname", advanced: false },
+              },
+              ...PROFILE_SCHEMA,
+            },
+          },
+        });
+      }
+      if (url.endsWith("/config")) {
+        return Promise.resolve({
+          data: { success: true, data: { server: serverSectionData, profile: PROFILE_SECTION } },
+        });
+      }
+      if (url.includes("/config/server")) {
+        return Promise.resolve({ data: { success: true, data: serverSectionData } });
+      }
+      if (url.includes("/config/profile")) {
+        return Promise.resolve({ data: { success: true, data: PROFILE_SECTION } });
+      }
+      return Promise.resolve({ data: { success: true, data: {} } });
+    });
+  }
+
+  it("shows profile warning banner when difficulty is not Custom", async () => {
+    mockWithDifficulty("Regular");
+    render(<ConfigEditor serverId={1} />, { wrapper: createWrapper() });
+
+    // Switch to Difficulty tab
+    await screen.findByText("Difficulty");
+    fireEvent.click(screen.getByText("Difficulty"));
+
+    await screen.findByText(/only apply when/i);
+  });
+
+  it("does not show profile warning banner when difficulty is Custom", async () => {
+    mockWithDifficulty("Custom");
+    render(<ConfigEditor serverId={1} />, { wrapper: createWrapper() });
+
+    await screen.findByText("Difficulty");
+    fireEvent.click(screen.getByText("Difficulty"));
+
+    // Fields should show without the gating banner
+    await screen.findByText("Group Indicators");
+    expect(screen.queryByText(/only apply when/i)).not.toBeInTheDocument();
+  });
+});
diff --git a/frontend/src/components/servers/ConfigEditor.tsx b/frontend/src/components/servers/ConfigEditor.tsx
index 69a9b1c..6259f29 100644
--- a/frontend/src/components/servers/ConfigEditor.tsx
+++ b/frontend/src/components/servers/ConfigEditor.tsx
@@ -35,6 +35,7 @@ export function ConfigEditor({ serverId }: ConfigEditorProps) {
   const isAdmin = useAuthStore((s) => s.user?.role === "admin");
   const addNotification = useUIStore((s) => s.addNotification);
   const { data: configMap, isLoading } = useServerConfig(serverId);
+  const { data: schema } = useServerConfigSchema(serverId);
 
   const sections = configMap ? Object.keys(configMap).filter((k) => k !== "_meta") : [];
   const [activeSection, setActiveSection] = useState<string>(sections[0] ?? "");
@@ -49,6 +50,11 @@ export function ConfigEditor({ serverId }: ConfigEditorProps) {
 
   const currentSection = activeSection || sections[0];
 
+  // Derive forced_difficulty from server section for profile gate
+  const serverSection = configMap["server"] as Record<string, unknown> | undefined;
+  const forcedDifficulty = serverSection?.["forced_difficulty"] as string | undefined;
+  const profileGated = currentSection === "profile" && forcedDifficulty !== "Custom";
+
   return (
     <div data-testid="config-editor">
       <div className="flex gap-1 mb-3 overflow-x-auto">
@@ -72,11 +78,18 @@ export function ConfigEditor({ serverId }: ConfigEditorProps) {
         <p className="text-text-muted text-xs mb-4">{SECTION_DESCRIPTIONS[currentSection]}</p>
       )}
 
+      {profileGated && (
+        <div className="rounded-lg border border-surface-raised bg-surface-overlay px-4 py-3 mb-4 text-sm text-text-secondary">
+          These settings only apply when <strong>Forced Difficulty</strong> is set to <strong>Custom</strong> in the Server tab. Current value: <em>{forcedDifficulty ?? "—"}</em>
+        </div>
+      )}
+
       {currentSection && (
         <ConfigSectionForm
           key={currentSection}
           serverId={serverId}
           section={currentSection}
+          sectionSchema={schema?.[currentSection] ?? {}}
           isAdmin={isAdmin}
           addNotification={addNotification}
         />
@@ -88,19 +101,21 @@ export function ConfigEditor({ serverId }: ConfigEditorProps) {
 function ConfigSectionForm({
   serverId,
   section,
+  sectionSchema,
   isAdmin,
   addNotification,
 }: {
   serverId: number;
   section: string;
+  sectionSchema: Record<string, FieldSchema>;
   isAdmin: boolean;
   addNotification: (n: { type: "success" | "error" | "info" | "warning"; message: string }) => void;
 }) {
   const { data: sectionData, isLoading } = useServerConfigSection(serverId, section);
-  const { data: schema } = useServerConfigSchema(serverId);
   const updateSection = useUpdateConfigSection(serverId, section);
   const [editValues, setEditValues] = useState<Record<string, unknown> | null>(null);
   const [showPassword, setShowPassword] = useState<Record<string, boolean>>({});
+  const [showAdvanced, setShowAdvanced] = useState(false);
 
   if (isLoading) {
     return <div className="text-text-muted text-sm">Loading section...</div>;
@@ -110,12 +125,23 @@ function ConfigSectionForm({
     return <div className="text-text-muted text-sm">No data for this section.</div>;
   }
 
-  const sectionSchema = schema?.[section] ?? {};
-  const fields = Object.entries(sectionData).filter(([key]) => {
+  const hasAdvancedFields = Object.values(sectionSchema).some((f) => f.advanced === true);
+
+  const allFields = Object.entries(sectionData).filter(([key]) => {
     if (key === "_meta") return false;
     if (sectionSchema[key]?.widget === "hidden") return false;
     return true;
   });
+
+  // When schema has advanced flags, filter by them; otherwise show everything
+  const schemaHasFlags = Object.keys(sectionSchema).length > 0 && Object.values(sectionSchema).some((f) => "advanced" in f);
+  const fields = schemaHasFlags
+    ? allFields.filter(([key]) => {
+        const fieldSchema = sectionSchema[key];
+        if (!fieldSchema || fieldSchema.advanced === undefined) return true;
+        return showAdvanced ? true : !fieldSchema.advanced;
+      })
+    : allFields;
   const meta = sectionData._meta;
   const displayValues = editValues ?? Object.fromEntries(fields);
   const isEditing = editValues !== null;
@@ -131,7 +157,11 @@ function ConfigSectionForm({
   };
 
   const handleSave = async () => {
-    if (!editValues || !meta) return;
+    if (!editValues) return;
+    if (!meta) {
+      addNotification({ type: "error", message: "Cannot save: config metadata is missing. Please refresh the page." });
+      return;
+    }
     try {
       await updateSection.mutateAsync({
         config_version: meta.config_version,
@@ -167,9 +197,19 @@ function ConfigSectionForm({
   return (
     <div className="space-y-3">
       <div className="flex items-center justify-between mb-2">
-        <p className="text-text-muted text-xs">
-          Version: {meta?.config_version ?? "--"} | Schema: {meta?.schema_version ?? "--"}
-        </p>
+        <div className="flex items-center gap-3">
+          <p className="text-text-muted text-xs">
+            Version: {meta?.config_version ?? "--"} | Schema: {meta?.schema_version ?? "--"}
+          </p>
+          {hasAdvancedFields && !isEditing && (
+            <button
+              onClick={() => setShowAdvanced((v) => !v)}
+              className="text-xs text-text-secondary hover:text-text-primary underline underline-offset-2"
+            >
+              {showAdvanced ? "Hide advanced" : "Show advanced"}
+            </button>
+          )}
+        </div>
         {isAdmin && !isEditing && (
           <button onClick={handleEdit} className="btn-ghost text-sm">
             Edit
@@ -197,7 +237,7 @@ function ConfigSectionForm({
                 onChange={(v) => handleChange(key, v)}
               />
             ) : widget === "toggle" ? (
-              <div className="flex-1 px-3 py-2">
+              <div className="flex items-center flex-1 px-1">
                 <ToggleDisplay value={rawValue} />
               </div>
             ) : widget === "select" ? (
@@ -267,9 +307,11 @@ function FieldWidget({
       const options = fieldSchema?.options ?? [];
       // Options may use "N - Description" format for numeric fields
       const isNumericOptions = options.length > 0 && /^\d+ /.test(options[0]);
-      const selectedOpt = isNumericOptions
-        ? (options.find((opt) => parseInt(opt, 10) === Number(value)) ?? String(value ?? ""))
-        : String(value ?? "");
+      const matchedOpt = isNumericOptions
+        ? options.find((opt) => parseInt(opt, 10) === Number(value))
+        : options.find((opt) => opt === String(value ?? ""));
+      // Fall back to first option when stored value has no match (avoids silent blank selection)
+      const selectedOpt = matchedOpt ?? options[0] ?? String(value ?? "");
       return (
         <select
           className="neu-input flex-1 text-sm"
@@ -293,11 +335,9 @@ function FieldWidget({
 
     case "toggle":
       return (
-        <input
-          type="checkbox"
-          className="w-5 h-5 accent-accent"
+        <ToggleSwitch
           checked={value === true || value === 1 || value === "true"}
-          onChange={(e) => onChange(e.target.checked ? 1 : 0)}
+          onChange={(checked) => onChange(checked ? 1 : 0)}
         />
       );
 
@@ -323,10 +363,13 @@ function FieldWidget({
         <input
           type="number"
           className="neu-input flex-1 text-sm"
-          value={String(value ?? "")}
+          value={value === null || value === undefined ? "" : String(value)}
           min={fieldSchema?.min}
           max={fieldSchema?.max}
-          onChange={(e) => onChange(Number(e.target.value))}
+          onChange={(e) => {
+            const v = e.target.value;
+            onChange(v === "" ? null : Number(v));
+          }}
         />
       );
 
@@ -362,13 +405,50 @@ function FieldWidget({
   }
 }
 
+function ToggleSwitch({ checked, onChange }: { checked: boolean; onChange: (v: boolean) => void }) {
+  return (
+    <button
+      type="button"
+      role="switch"
+      aria-checked={checked}
+      onClick={() => onChange(!checked)}
+      className={clsx(
+        "relative inline-flex h-6 w-11 shrink-0 items-center rounded-full",
+        "transition-colors duration-200 focus:outline-none focus:ring-2 focus:ring-accent focus:ring-offset-1 focus:ring-offset-surface-base",
+        checked
+          ? "bg-accent shadow-glow-amber"
+          : "bg-surface-overlay border border-surface-raised shadow-neu-recessed",
+      )}
+    >
+      <span
+        className={clsx(
+          "inline-block h-4 w-4 rounded-full shadow-md transform transition-transform duration-200",
+          checked ? "translate-x-6 bg-text-inverse" : "translate-x-1 bg-text-muted",
+        )}
+      />
+    </button>
+  );
+}
+
 function ToggleDisplay({ value }: { value: unknown }) {
   const on = value === true || value === 1 || value === "true" || value === "1";
   return (
-    <span className={clsx("inline-flex items-center gap-1.5 text-sm font-sans", on ? "text-green-400" : "text-text-muted")}>
-      <span className={clsx("w-3 h-3 rounded-full", on ? "bg-green-400" : "bg-surface-overlay border border-text-muted")} />
-      {on ? "Enabled" : "Disabled"}
-    </span>
+    <div
+      className={clsx(
+        "relative inline-flex h-6 w-11 shrink-0 items-center rounded-full cursor-not-allowed opacity-75",
+        on
+          ? "bg-accent shadow-glow-amber"
+          : "bg-surface-overlay border border-surface-raised shadow-neu-recessed",
+      )}
+      aria-hidden="true"
+    >
+      <span
+        className={clsx(
+          "inline-block h-4 w-4 rounded-full shadow-md transform",
+          on ? "translate-x-6 bg-text-inverse" : "translate-x-1 bg-text-muted",
+        )}
+      />
+    </div>
   );
 }
 
diff --git a/frontend/src/hooks/useServerDetail.ts b/frontend/src/hooks/useServerDetail.ts
index fe14558..7ee375e 100644
--- a/frontend/src/hooks/useServerDetail.ts
+++ b/frontend/src/hooks/useServerDetail.ts
@@ -124,10 +124,16 @@ export interface Mod {
   path: string;
   size_bytes: number;
   enabled: boolean;
+  is_server_mod: boolean;
   display_name: string | null;
   workshop_id: string | null;
 }
 
+export interface EnabledModEntry {
+  name: string;
+  is_server_mod: boolean;
+}
+
 export interface FieldSchema {
   widget: "text" | "number" | "password" | "textarea" | "select" | "toggle" | "tag-list" | "hidden" | "key-value";
   label?: string;
@@ -135,6 +141,7 @@ export interface FieldSchema {
   min?: number;
   max?: number;
   options?: string[];
+  advanced?: boolean;
 }
 
 export interface ConfigSchema {
@@ -380,7 +387,7 @@ export function useDeleteMission(serverId: number) {
 export function useSetEnabledMods(serverId: number) {
   const queryClient = useQueryClient();
   return useMutation({
-    mutationFn: (mods: string[]) =>
+    mutationFn: (mods: EnabledModEntry[]) =>
       apiClient.put(`/api/servers/${serverId}/mods/enabled`, { mods }),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["mods", serverId] });