diff --git a/DNSecure/DNSecureApp.swift b/DNSecure/DNSecureApp.swift
index a2f1927..6ccd314 100644
--- a/DNSecure/DNSecureApp.swift
+++ b/DNSecure/DNSecureApp.swift
@@ -5,15 +5,15 @@
 //  Created by Kenta Kubo on 7/1/20.
 //
 
-import os
+import os.log
 import SwiftUI
 
 let logger = Logger()
 
 @main
 struct DNSecureApp {
-    @AppStorage("servers") var servers = Presets.servers
-    @AppStorage("usedID") var usedID: String?
+    @AppStorage("servers") private var servers = Presets.servers
+    @AppStorage("usedID") private var usedID: String?
 }
 
 extension DNSecureApp: App {
diff --git a/DNSecure/Models/Resolver.swift b/DNSecure/Models/Resolver.swift
index 6c19022..4e71140 100644
--- a/DNSecure/Models/Resolver.swift
+++ b/DNSecure/Models/Resolver.swift
@@ -61,11 +61,11 @@ extension Configuration: Equatable {}
 extension Configuration: Hashable {}
 
 extension Configuration: Codable {
-    enum CodingKeys: String, CodingKey {
+    private enum CodingKeys: String, CodingKey {
         case base, dotConfiguration, dohConfiguration
     }
 
-    enum Base: String, Codable {
+    private enum Base: String, Codable {
         case dnsOverTLS, dnsOverHTTPS
     }
 
@@ -191,12 +191,12 @@ extension Resolver: Equatable {}
 extension Resolver: Hashable {}
 
 extension Resolver: Codable {
-    enum CodingKeys: String, CodingKey {
+    private enum CodingKeys: String, CodingKey {
         case id, name, configuration, onDemandRules
     }
 
     init(from decoder: Decoder) throws {
-        let container = try decoder.container(keyedBy: CodingKeys.self)
+        let container = try decoder.container(keyedBy: Self.CodingKeys.self)
         self.id = try container.decode(UUID.self, forKey: .id)
         self.name = try container.decode(String.self, forKey: .name)
         self.configuration = try container.decode(Configuration.self, forKey: .configuration)
diff --git a/DNSecure/Views/ContentView.swift b/DNSecure/Views/ContentView.swift
index 4b9e7b7..b551a29 100644
--- a/DNSecure/Views/ContentView.swift
+++ b/DNSecure/Views/ContentView.swift
@@ -9,17 +9,17 @@ import NetworkExtension
 import SwiftUI
 
 struct ContentView {
-    @Environment(\.scenePhase) var scenePhase
+    @Environment(\.scenePhase) private var scenePhase
     @Binding var servers: Resolvers
     @Binding var usedID: String?
-    @State var isEnabled = false
-    @State var selection: Int?
-    @State var alertIsPresented = false
-    @State var alertTitle = ""
-    @State var alertMessage = ""
-    @State var guideIsPresented = false
+    @State private var isEnabled = false
+    @State private var selection: Int?
+    @State private var alertIsPresented = false
+    @State private var alertTitle = ""
+    @State private var alertMessage = ""
+    @State private var guideIsPresented = false
 
-    func addNewDoTServer() {
+    private func addNewDoTServer() {
         self.servers.append(
             .init(
                 name: "New",
@@ -29,7 +29,7 @@ struct ContentView {
         self.selection = self.servers.count - 1
     }
 
-    func addNewDoHServer() {
+    private func addNewDoHServer() {
         self.servers.append(
             .init(
                 name: "New",
@@ -39,7 +39,7 @@ struct ContentView {
         self.selection = self.servers.count - 1
     }
 
-    func removeServers(at indexSet: IndexSet) {
+    private func removeServers(at indexSet: IndexSet) {
         if let current = self.selection, indexSet.contains(where: { $0 <= current }) {
             // FIXME: This is a workaround not to crash on deletion.
             self.selection = -1
@@ -54,12 +54,12 @@ struct ContentView {
         }
     }
 
-    func moveServers(from src: IndexSet, to dst: Int) {
+    private func moveServers(from src: IndexSet, to dst: Int) {
         // TODO: Change self.selection if needed
         self.servers.move(fromOffsets: src, toOffset: dst)
     }
 
-    func updateStatus() {
+    private func updateStatus() {
         #if !targetEnvironment(simulator)
             let manager = NEDNSSettingsManager.shared()
             manager.loadFromPreferences {
@@ -73,7 +73,7 @@ struct ContentView {
         #endif
     }
 
-    func saveSettings(of server: Resolver) {
+    private func saveSettings(of server: Resolver) {
         if self.usedID != server.id.uuidString {
             self.usedID = server.id.uuidString
         }
@@ -99,7 +99,7 @@ struct ContentView {
         #endif
     }
 
-    func removeSettings() {
+    private func removeSettings() {
         self.usedID = nil
 
         #if !targetEnvironment(simulator)
@@ -120,7 +120,7 @@ struct ContentView {
         #endif
     }
 
-    func alert(_ title: String, _ message: String) {
+    private func alert(_ title: String, _ message: String) {
         self.alertTitle = title
         self.alertMessage = message
         self.alertIsPresented = true
diff --git a/DNSecure/Views/DetailView.swift b/DNSecure/Views/DetailView.swift
index 5f0edcd..140f7f9 100644
--- a/DNSecure/Views/DetailView.swift
+++ b/DNSecure/Views/DetailView.swift
@@ -11,7 +11,7 @@ struct DetailView {
     @Binding var server: Resolver
     @Binding var isOn: Bool
 
-    func binding(for rule: OnDemandRule) -> Binding<OnDemandRule> {
+    private func binding(for rule: OnDemandRule) -> Binding<OnDemandRule> {
         guard let index = self.server.onDemandRules.firstIndex(of: rule) else {
             preconditionFailure("Can't find rule in array")
         }
diff --git a/DNSecure/Views/HowToActivateView.swift b/DNSecure/Views/HowToActivateView.swift
index f557d1f..f9d16b3 100644
--- a/DNSecure/Views/HowToActivateView.swift
+++ b/DNSecure/Views/HowToActivateView.swift
@@ -8,7 +8,7 @@
 import SwiftUI
 
 struct HowToActivateView {
-    @Environment(\.presentationMode) var presentationMode
+    @Environment(\.presentationMode) private var presentationMode
     @State var isSheet: Bool
 }