diff --git a/AK/JsonObject.h b/AK/JsonObject.h
index 5b95005495bec6..aa177da18dbd78 100644
--- a/AK/JsonObject.h
+++ b/AK/JsonObject.h
@@ -41,26 +41,32 @@ class JsonObject {
     ~JsonObject() {}
 
     JsonObject(const JsonObject& other)
-        : m_members(other.m_members)
+        : m_order(other.m_order)
+        , m_members(other.m_members)
     {
     }
 
     JsonObject(JsonObject&& other)
-        : m_members(move(other.m_members))
+        : m_order(move(other.m_order))
+        , m_members(move(other.m_members))
     {
     }
 
     JsonObject& operator=(const JsonObject& other)
     {
-        if (this != &other)
+        if (this != &other) {
             m_members = other.m_members;
+            m_order = other.m_order;
+        }
         return *this;
     }
 
     JsonObject& operator=(JsonObject&& other)
     {
-        if (this != &other)
+        if (this != &other) {
             m_members = move(other.m_members);
+            m_order = move(other.m_order);
+        }
         return *this;
     }
 
@@ -70,7 +76,7 @@ class JsonObject {
     JsonValue get(const String& key) const
     {
         auto* value = get_ptr(key);
-        return value ? *value : JsonValue(JsonValue::Type::Undefined);
+        return value ? *value : JsonValue(JsonValue::Type::Null);
     }
 
     JsonValue get_or(const String& key, JsonValue alternative) const
@@ -94,14 +100,17 @@ class JsonObject {
 
     void set(const String& key, JsonValue value)
     {
+        m_order.append(key);
         m_members.set(key, move(value));
     }
 
     template<typename Callback>
     void for_each_member(Callback callback) const
     {
-        for (auto& it : m_members)
-            callback(it.key, it.value);
+        for (size_t i = 0; i < m_order.size(); ++i) {
+            auto property = m_order[i];
+            callback(property, m_members.get(property).value());
+        }
     }
 
     template<typename Builder>
@@ -113,6 +122,7 @@ class JsonObject {
     String to_string() const { return serialized<StringBuilder>(); }
 
 private:
+    Vector<String> m_order;
     HashMap<String, JsonValue> m_members;
 };
 
@@ -193,9 +203,6 @@ inline void JsonValue::serialize(Builder& builder) const
     case Type::UnsignedInt64:
         builder.appendf("%llu", as_u64());
         break;
-    case Type::Undefined:
-        builder.append("undefined");
-        break;
     case Type::Null:
         builder.append("null");
         break;
diff --git a/AK/JsonParser.cpp b/AK/JsonParser.cpp
index 7a883a8b3adb85..142c797a4792cc 100644
--- a/AK/JsonParser.cpp
+++ b/AK/JsonParser.cpp
@@ -62,15 +62,16 @@ void JsonParser::consume_whitespace()
     consume_while([](char ch) { return is_whitespace(ch); });
 }
 
-void JsonParser::consume_specific(char expected_ch)
+bool JsonParser::consume_specific(char expected_ch)
 {
     char consumed_ch = consume();
-    ASSERT(consumed_ch == expected_ch);
+    return consumed_ch == expected_ch;
 }
 
 String JsonParser::consume_quoted_string()
 {
-    consume_specific('"');
+    if (!consume_specific('"'))
+        return {};
     Vector<char, 1024> buffer;
 
     for (;;) {
@@ -136,7 +137,8 @@ String JsonParser::consume_quoted_string()
             break;
         }
     }
-    consume_specific('"');
+    if (!consume_specific('"'))
+        return {};
 
     if (buffer.is_empty())
         return String::empty();
@@ -151,55 +153,78 @@ String JsonParser::consume_quoted_string()
     return last_string_starting_with_character;
 }
 
-JsonObject JsonParser::parse_object()
+Optional<JsonValue> JsonParser::parse_object()
 {
     JsonObject object;
-    consume_specific('{');
+    if (!consume_specific('{'))
+        return {};
     for (;;) {
         consume_whitespace();
         if (peek() == '}')
             break;
         consume_whitespace();
         auto name = consume_quoted_string();
+        if (name.is_null())
+            return {};
         consume_whitespace();
-        consume_specific(':');
+        if (!consume_specific(':'))
+            return {};
         consume_whitespace();
-        auto value = parse();
-        object.set(name, move(value));
+        auto value = parse_helper();
+        if (!value.has_value())
+            return {};
+        object.set(name, move(value.value()));
         consume_whitespace();
         if (peek() == '}')
             break;
-        consume_specific(',');
+        if (!consume_specific(','))
+            return {};
+        consume_whitespace();
+        if (peek() == '}')
+            return {};
     }
-    consume_specific('}');
+    if (!consume_specific('}'))
+        return {};
     return object;
 }
 
-JsonArray JsonParser::parse_array()
+Optional<JsonValue> JsonParser::parse_array()
 {
     JsonArray array;
-    consume_specific('[');
+    if (!consume_specific('['))
+        return {};
     for (;;) {
         consume_whitespace();
         if (peek() == ']')
             break;
-        array.append(parse());
+        auto element = parse_helper();
+        if (!element.has_value())
+            return {};
+        array.append(element.value());
         consume_whitespace();
         if (peek() == ']')
             break;
-        consume_specific(',');
+        if (!consume_specific(','))
+            return {};
+        consume_whitespace();
+        if (peek() == ']')
+            return {};
     }
     consume_whitespace();
-    consume_specific(']');
+    if (!consume_specific(']'))
+        return {};
     return array;
 }
 
-JsonValue JsonParser::parse_string()
+Optional<JsonValue> JsonParser::parse_string()
 {
-    return consume_quoted_string();
+    auto result = consume_quoted_string();
+    if (result.is_null())
+        return {};
+    return JsonValue(result);
 }
 
-JsonValue JsonParser::parse_number()
+Optional<JsonValue> JsonParser::parse_number()
 {
     JsonValue value;
     Vector<char, 128> number_buffer;
@@ -235,7 +260,10 @@ JsonValue JsonParser::parse_number()
         if (to_signed_result.has_value()) {
             whole = to_signed_result.value();
         } else {
-            whole = number_string.to_int().value();
+            auto number = number_string.to_int();
+            if (!number.has_value())
+                return {};
+            whole = number.value();
         }
 
         int fraction = fraction_string.to_uint().value();
@@ -252,7 +280,10 @@ JsonValue JsonParser::parse_number()
         if (to_unsigned_result.has_value()) {
             value = JsonValue(to_unsigned_result.value());
         } else {
-            value = JsonValue(number_string.to_int().value());
+            auto number = number_string.to_int();
+            if (!number.has_value())
+                return {};
+            value = JsonValue(number.value());
         }
 #ifndef KERNEL
     }
@@ -261,37 +292,37 @@ JsonValue JsonParser::parse_number()
     return value;
 }
 
-void JsonParser::consume_string(const char* str)
+bool JsonParser::consume_string(const char* str)
 {
-    for (size_t i = 0, length = strlen(str); i < length; ++i)
-        consume_specific(str[i]);
+    for (size_t i = 0, length = strlen(str); i < length; ++i) {
+        if (!consume_specific(str[i]))
+            return false;
+    }
+    return true;
 }
 
-JsonValue JsonParser::parse_true()
+Optional<JsonValue> JsonParser::parse_true()
 {
-    consume_string("true");
+    if (!consume_string("true"))
+        return {};
     return JsonValue(true);
 }
 
-JsonValue JsonParser::parse_false()
+Optional<JsonValue> JsonParser::parse_false()
 {
-    consume_string("false");
+    if (!consume_string("false"))
+        return {};
     return JsonValue(false);
 }
 
-JsonValue JsonParser::parse_null()
+Optional<JsonValue> JsonParser::parse_null()
 {
-    consume_string("null");
+    if (!consume_string("null"))
+        return {};
     return JsonValue(JsonValue::Type::Null);
 }
 
-JsonValue JsonParser::parse_undefined()
-{
-    consume_string("undefined");
-    return JsonValue(JsonValue::Type::Undefined);
-}
-
-JsonValue JsonParser::parse()
+Optional<JsonValue> JsonParser::parse_helper()
 {
     consume_whitespace();
     auto type_hint = peek();
@@ -320,10 +351,19 @@ JsonValue JsonParser::parse()
         return parse_true();
     case 'n':
         return parse_null();
-    case 'u':
-        return parse_undefined();
     }
 
-    return JsonValue();
+    return {};
+}
+
+Optional<JsonValue> JsonParser::parse() {
+    auto result = parse_helper();
+    if (!result.has_value())
+        return {};
+    consume_whitespace();
+    if (m_index != m_input.length())
+        return {};
+    return result;
 }
+
 }
diff --git a/AK/JsonParser.h b/AK/JsonParser.h
index 3ff321424ca38f..607bab8a6fc879 100644
--- a/AK/JsonParser.h
+++ b/AK/JsonParser.h
@@ -40,23 +40,24 @@ class JsonParser {
     {
     }
 
-    JsonValue parse();
+    Optional<JsonValue> parse();
 
 private:
+    Optional<JsonValue> parse_helper();
+
     char peek() const;
     char consume();
     void consume_whitespace();
-    void consume_specific(char expected_ch);
-    void consume_string(const char*);
+    bool consume_specific(char expected_ch);
+    bool consume_string(const char*);
     String consume_quoted_string();
-    JsonArray parse_array();
-    JsonObject parse_object();
-    JsonValue parse_number();
-    JsonValue parse_string();
-    JsonValue parse_false();
-    JsonValue parse_true();
-    JsonValue parse_null();
-    JsonValue parse_undefined();
+    Optional<JsonValue> parse_array();
+    Optional<JsonValue> parse_object();
+    Optional<JsonValue> parse_number();
+    Optional<JsonValue> parse_string();
+    Optional<JsonValue> parse_false();
+    Optional<JsonValue> parse_true();
+    Optional<JsonValue> parse_null();
 
     template<typename C>
     void consume_while(C);
diff --git a/AK/JsonValue.cpp b/AK/JsonValue.cpp
index 76e65f3f15eac4..8a1bc99f04e2b9 100644
--- a/AK/JsonValue.cpp
+++ b/AK/JsonValue.cpp
@@ -75,7 +75,7 @@ void JsonValue::copy_from(const JsonValue& other)
 
 JsonValue::JsonValue(JsonValue&& other)
 {
-    m_type = exchange(other.m_type, Type::Undefined);
+    m_type = exchange(other.m_type, Type::Null);
     m_value.as_string = exchange(other.m_value.as_string, nullptr);
 }
 
@@ -83,7 +83,7 @@ JsonValue& JsonValue::operator=(JsonValue&& other)
 {
     if (this != &other) {
         clear();
-        m_type = exchange(other.m_type, Type::Undefined);
+        m_type = exchange(other.m_type, Type::Null);
         m_value.as_string = exchange(other.m_value.as_string, nullptr);
     }
     return *this;
@@ -247,11 +247,11 @@ void JsonValue::clear()
     default:
         break;
     }
-    m_type = Type::Undefined;
+    m_type = Type::Null;
     m_value.as_string = nullptr;
 }
 
-JsonValue JsonValue::from_string(const StringView& input)
+Optional<JsonValue> JsonValue::from_string(const StringView& input)
 {
     return JsonParser(input).parse();
 }
diff --git a/AK/JsonValue.h b/AK/JsonValue.h
index 5ff6b4be997248..7d3eef87f997bd 100644
--- a/AK/JsonValue.h
+++ b/AK/JsonValue.h
@@ -37,7 +37,6 @@ namespace AK {
 class JsonValue {
 public:
     enum class Type {
-        Undefined,
         Null,
         Int32,
         UnsignedInt32,
@@ -52,7 +51,7 @@ class JsonValue {
         Object,
     };
 
-    static JsonValue from_string(const StringView&);
+    static Optional<JsonValue> from_string(const StringView&);
 
     explicit JsonValue(Type = Type::Null);
     ~JsonValue() { clear(); }
@@ -188,7 +187,6 @@ class JsonValue {
     }
 
     bool is_null() const { return m_type == Type::Null; }
-    bool is_undefined() const { return m_type == Type::Undefined; }
     bool is_bool() const { return m_type == Type::Bool; }
     bool is_string() const { return m_type == Type::String; }
     bool is_i32() const { return m_type == Type::Int32; }
@@ -246,7 +244,7 @@ class JsonValue {
     void clear();
     void copy_from(const JsonValue&);
 
-    Type m_type { Type::Undefined };
+    Type m_type { Type::Null };
 
     union {
         StringImpl* as_string { nullptr };
diff --git a/AK/Tests/TestJSON.cpp b/AK/Tests/TestJSON.cpp
index c8e787d4d47223..87dca328794c1e 100644
--- a/AK/Tests/TestJSON.cpp
+++ b/AK/Tests/TestJSON.cpp
@@ -48,7 +48,7 @@ TEST_CASE(load_form)
 
     fclose(fp);
 
-    JsonValue form_json = JsonValue::from_string(builder.to_string());
+    JsonValue form_json = JsonValue::from_string(builder.to_string()).value();
 
     EXPECT(form_json.is_object());
 
@@ -87,14 +87,14 @@ BENCHMARK_CASE(load_4chan_catalog)
     auto json_string = builder.to_string();
 
     for (int i = 0; i < 10; ++i) {
-        JsonValue form_json = JsonValue::from_string(json_string);
+        JsonValue form_json = JsonValue::from_string(json_string).value();
         EXPECT(form_json.is_array());
     }
 }
 
 TEST_CASE(json_empty_string)
 {
-    auto json = JsonValue::from_string("\"\"");
+    auto json = JsonValue::from_string("\"\"").value();
     EXPECT_EQ(json.type(), JsonValue::Type::String);
     EXPECT_EQ(json.as_string().is_null(), false);
     EXPECT_EQ(json.as_string().is_empty(), true);
@@ -102,7 +102,7 @@ TEST_CASE(json_empty_string)
 
 TEST_CASE(json_utf8_character)
 {
-    auto json = JsonValue::from_string("\"\xc3\x84\"");
+    auto json = JsonValue::from_string("\"\xc3\x84\"").value();
     EXPECT_EQ(json.type(), JsonValue::Type::String);
     EXPECT_EQ(json.as_string().is_null(), false);
     EXPECT_EQ(json.as_string().length(), size_t { 2 });
diff --git a/Applications/SystemMonitor/DevicesModel.cpp b/Applications/SystemMonitor/DevicesModel.cpp
index 69091402cc686f..5777d0f601b8c5 100644
--- a/Applications/SystemMonitor/DevicesModel.cpp
+++ b/Applications/SystemMonitor/DevicesModel.cpp
@@ -127,10 +127,11 @@ void DevicesModel::update()
     if (!proc_devices->open(Core::IODevice::OpenMode::ReadOnly))
         ASSERT_NOT_REACHED();
 
-    auto json = JsonValue::from_string(proc_devices->read_all()).as_array();
+    auto json = JsonValue::from_string(proc_devices->read_all());
+    ASSERT(json.has_value());
 
     m_devices.clear();
-    json.for_each([this](auto& value) {
+    json.value().as_array().for_each([this](auto& value) {
         JsonObject device = value.as_object();
         DeviceInfo device_info;
 
diff --git a/Applications/SystemMonitor/MemoryStatsWidget.cpp b/Applications/SystemMonitor/MemoryStatsWidget.cpp
index c9ebacc2687f97..89bd77fdc49709 100644
--- a/Applications/SystemMonitor/MemoryStatsWidget.cpp
+++ b/Applications/SystemMonitor/MemoryStatsWidget.cpp
@@ -98,7 +98,9 @@ void MemoryStatsWidget::refresh()
         ASSERT_NOT_REACHED();
 
     auto file_contents = proc_memstat->read_all();
-    auto json = JsonValue::from_string(file_contents).as_object();
+    auto json_result = JsonValue::from_string(file_contents);
+    ASSERT(json_result.has_value());
+    auto json = json_result.value().as_object();
 
     unsigned kmalloc_eternal_allocated = json.get("kmalloc_eternal_allocated").to_u32();
     (void)kmalloc_eternal_allocated;
diff --git a/DevTools/FormCompiler/main.cpp b/DevTools/FormCompiler/main.cpp
index 0ccafa31ce8929..7113f510fc709b 100644
--- a/DevTools/FormCompiler/main.cpp
+++ b/DevTools/FormCompiler/main.cpp
@@ -46,7 +46,9 @@ int main(int argc, char** argv)
     }
 
     auto file_contents = file->read_all();
-    auto json = JsonValue::from_string(file_contents);
+    auto json_result = JsonValue::from_string(file_contents);
+    ASSERT(json_result.has_value());
+    auto json = json_result.value();
 
     if (!json.is_object()) {
         fprintf(stderr, "Malformed input\n");
diff --git a/DevTools/Inspector/RemoteProcess.cpp b/DevTools/Inspector/RemoteProcess.cpp
index d1ceb61c3dfd79..6e8dce589497ae 100644
--- a/DevTools/Inspector/RemoteProcess.cpp
+++ b/DevTools/Inspector/RemoteProcess.cpp
@@ -167,11 +167,12 @@ void RemoteProcess::update()
         dbg() << "Got data size " << length << " and read that many bytes";
 
         auto json_value = JsonValue::from_string(data);
-        ASSERT(json_value.is_object());
+        ASSERT(json_value.has_value());
+        ASSERT(json_value.value().is_object());
 
-        dbg() << "Got JSON response " << json_value.to_string();
+        dbg() << "Got JSON response " << json_value.value().to_string();
 
-        auto& response = json_value.as_object();
+        auto& response = json_value.value().as_object();
 
         auto response_type = response.get("type").as_string_or({});
         if (response_type.is_null())
diff --git a/DevTools/ProfileViewer/Profile.cpp b/DevTools/ProfileViewer/Profile.cpp
index 435bfd28105314..32c966bbb5c63c 100644
--- a/DevTools/ProfileViewer/Profile.cpp
+++ b/DevTools/ProfileViewer/Profile.cpp
@@ -172,12 +172,13 @@ OwnPtr<Profile> Profile::load_from_perfcore_file(const StringView& path)
     }
 
     auto json = JsonValue::from_string(file->read_all());
-    if (!json.is_object()) {
+    ASSERT(json.has_value());
+    if (!json.value().is_object()) {
         fprintf(stderr, "Invalid perfcore format (not a JSON object)\n");
         return nullptr;
     }
 
-    auto& object = json.as_object();
+    auto& object = json.value().as_object();
     auto executable_path = object.get("executable").to_string();
 
     MappedFile elf_file(executable_path);
diff --git a/DevTools/VisualBuilder/VBForm.cpp b/DevTools/VisualBuilder/VBForm.cpp
index 7bd247c1882830..6f813a4e5554c8 100644
--- a/DevTools/VisualBuilder/VBForm.cpp
+++ b/DevTools/VisualBuilder/VBForm.cpp
@@ -389,14 +389,15 @@ void VBForm::load_from_file(const String& path)
 
     auto file_contents = file->read_all();
     auto form_json = JsonValue::from_string(file_contents);
+    ASSERT(form_json.has_value());
 
-    if (!form_json.is_object()) {
+    if (!form_json.value().is_object()) {
         GUI::MessageBox::show(String::format("Could not parse '%s'", path.characters()), "Error", GUI::MessageBox::Type::Error, GUI::MessageBox::InputType::OK, window());
         return;
     }
 
-    m_name = form_json.as_object().get("name").to_string();
-    auto widgets = form_json.as_object().get("widgets").as_array();
+    m_name = form_json.value().as_object().get("name").to_string();
+    auto widgets = form_json.value().as_object().get("widgets").as_array();
 
     widgets.for_each([&](const JsonValue& widget_value) {
         auto& widget_object = widget_value.as_object();
diff --git a/Libraries/LibCore/EventLoop.cpp b/Libraries/LibCore/EventLoop.cpp
index ebf457a3b87c65..a35da46b8b8015 100644
--- a/Libraries/LibCore/EventLoop.cpp
+++ b/Libraries/LibCore/EventLoop.cpp
@@ -105,13 +105,13 @@ class RPCClient : public Object {
             auto request = m_socket->read(length);
 
             auto request_json = JsonValue::from_string(request);
-            if (!request_json.is_object()) {
+            if (!request_json.has_value() || !request_json.value().is_object()) {
                 dbg() << "RPC client sent invalid request";
                 shutdown();
                 return;
             }
 
-            handle_request(request_json.as_object());
+            handle_request(request_json.value().as_object());
         };
     }
     virtual ~RPCClient() override
diff --git a/Libraries/LibCore/ProcessStatisticsReader.cpp b/Libraries/LibCore/ProcessStatisticsReader.cpp
index 13936b9f15b484..b9a55eb0c33fa1 100644
--- a/Libraries/LibCore/ProcessStatisticsReader.cpp
+++ b/Libraries/LibCore/ProcessStatisticsReader.cpp
@@ -48,7 +48,8 @@ HashMap<pid_t, Core::ProcessStatistics> ProcessStatisticsReader::get_all()
 
     auto file_contents = file->read_all();
     auto json = JsonValue::from_string(file_contents);
-    json.as_array().for_each([&](auto& value) {
+    ASSERT(json.has_value());
+    json.value().as_array().for_each([&](auto& value) {
         const JsonObject& process_object = value.as_object();
         Core::ProcessStatistics process;
 
diff --git a/Libraries/LibGUI/JsonArrayModel.cpp b/Libraries/LibGUI/JsonArrayModel.cpp
index fee86003ea3e50..e845602c145fb1 100644
--- a/Libraries/LibGUI/JsonArrayModel.cpp
+++ b/Libraries/LibGUI/JsonArrayModel.cpp
@@ -42,8 +42,9 @@ void JsonArrayModel::update()
 
     auto json = JsonValue::from_string(file->read_all());
 
-    ASSERT(json.is_array());
-    m_array = json.as_array();
+    ASSERT(json.has_value());
+    ASSERT(json.value().is_array());
+    m_array = json.value().as_array();
 
     did_update();
 }
diff --git a/Libraries/LibKeyboard/CharacterMapFile.cpp b/Libraries/LibKeyboard/CharacterMapFile.cpp
index c1ee2fa5b6bbd9..eb50e7f876629a 100644
--- a/Libraries/LibKeyboard/CharacterMapFile.cpp
+++ b/Libraries/LibKeyboard/CharacterMapFile.cpp
@@ -48,7 +48,9 @@ Optional<CharacterMapData> CharacterMapFile::load_from_file(const String& file_n
     }
 
     auto file_contents = file->read_all();
-    auto json = JsonValue::from_string(file_contents).as_object();
+    auto json_result = JsonValue::from_string(file_contents);
+    ASSERT(json_result.has_value());
+    auto json = json_result.value().as_object();
 
     ByteBuffer map = read_map(json, "map");
     ByteBuffer shift_map = read_map(json, "shift_map");
diff --git a/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_cpp.cpp b/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_cpp.cpp
index 9891d6bae43c99..7fab48f81d8b42 100644
--- a/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_cpp.cpp
+++ b/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_cpp.cpp
@@ -56,7 +56,8 @@ int main(int argc, char** argv)
         return 1;
 
     auto json = JsonValue::from_string(file->read_all());
-    ASSERT(json.is_object());
+    ASSERT(json.has_value());
+    ASSERT(json.value().is_object());
 
     out() << "#include <AK/Assertions.h>";
     out() << "#include <LibWeb/CSS/PropertyID.h>";
@@ -65,7 +66,7 @@ int main(int argc, char** argv)
 
     out() << "PropertyID property_id_from_string(const StringView& string) {";
 
-    json.as_object().for_each_member([&](auto& name, auto& value) {
+    json.value().as_object().for_each_member([&](auto& name, auto& value) {
         ASSERT(value.is_object());
         out() << "    if (string.equals_ignoring_case(\"" << name << "\"))";
         out() << "        return PropertyID::" << title_casify(name) << ";";
@@ -77,7 +78,7 @@ int main(int argc, char** argv)
 
     out() << "const char* string_from_property_id(PropertyID property_id) {";
     out() << "    switch (property_id) {";
-    json.as_object().for_each_member([&](auto& name, auto& value) {
+    json.value().as_object().for_each_member([&](auto& name, auto& value) {
         ASSERT(value.is_object());
         out() << "    case PropertyID::" << title_casify(name) << ":";
         out() << "        return \"" << name << "\";";
diff --git a/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp b/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp
index 04cd3d9278c693..1dbf80d9a30e75 100644
--- a/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp
+++ b/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp
@@ -56,7 +56,8 @@ int main(int argc, char** argv)
         return 1;
 
     auto json = JsonValue::from_string(file->read_all());
-    ASSERT(json.is_object());
+    ASSERT(json.has_value());
+    ASSERT(json.value().is_object());
 
     out() << "#pragma once";
     out() << "#include <AK/StringView.h>";
@@ -67,7 +68,7 @@ int main(int argc, char** argv)
     out() << "enum class PropertyID {";
     out() << "    Invalid,";
 
-    json.as_object().for_each_member([&](auto& name, auto& value) {
+    json.value().as_object().for_each_member([&](auto& name, auto& value) {
         ASSERT(value.is_object());
         out() << "    " << title_casify(name) << ",";
     });
diff --git a/MenuApplets/ResourceGraph/main.cpp b/MenuApplets/ResourceGraph/main.cpp
index d982d9f9e9e20f..2bea1acabc0351 100644
--- a/MenuApplets/ResourceGraph/main.cpp
+++ b/MenuApplets/ResourceGraph/main.cpp
@@ -140,9 +140,10 @@ class GraphWidget final : public GUI::Frame {
             ASSERT_NOT_REACHED();
 
         auto file_contents = proc_memstat->read_all();
-        auto json = JsonValue::from_string(file_contents).as_object();
-        unsigned user_physical_allocated = json.get("user_physical_allocated").to_u32();
-        unsigned user_physical_available = json.get("user_physical_available").to_u32();
+        auto json = JsonValue::from_string(file_contents);
+        ASSERT(json.has_value());
+        unsigned user_physical_allocated = json.value().as_object().get("user_physical_allocated").to_u32();
+        unsigned user_physical_available = json.value().as_object().get("user_physical_available").to_u32();
         allocated = (user_physical_allocated * 4096) / 1024;
         available = (user_physical_available * 4096) / 1024;
     }
diff --git a/Meta/Lagom/TestJson.cpp b/Meta/Lagom/TestJson.cpp
index 4c8891f0d9911f..e149daddf62e66 100644
--- a/Meta/Lagom/TestJson.cpp
+++ b/Meta/Lagom/TestJson.cpp
@@ -31,7 +31,8 @@
 int main(int, char**)
 {
     auto value = JsonValue::from_string("{\"property\": \"value\"}");
-    printf("parsed: _%s_\n", value.to_string().characters());
-    printf("object.property = '%s'\n", value.as_object().get("property").to_string().characters());
+    ASSERT(value.has_value());
+    printf("parsed: _%s_\n", value.value().to_string().characters());
+    printf("object.property = '%s'\n", value.value().as_object().get("property").to_string().characters());
     return 0;
 }
diff --git a/Services/DHCPClient/main.cpp b/Services/DHCPClient/main.cpp
index b65b63eb469f4b..33e7d7e2e8baac 100644
--- a/Services/DHCPClient/main.cpp
+++ b/Services/DHCPClient/main.cpp
@@ -77,9 +77,10 @@ int main(int argc, char** argv)
     }
 
     auto file_contents = file->read_all();
-    auto json = JsonValue::from_string(file_contents).as_array();
+    auto json = JsonValue::from_string(file_contents);
+    ASSERT(json.has_value());
     Vector<InterfaceDescriptor> ifnames;
-    json.for_each([&ifnames](auto& value) {
+    json.value().as_array().for_each([&ifnames](auto& value) {
         auto if_object = value.as_object();
 
         if (if_object.get("class_name").to_string() == "LoopbackAdapter")
diff --git a/Userland/arp.cpp b/Userland/arp.cpp
index 700302f73e8e7e..9f3149409a94bf 100644
--- a/Userland/arp.cpp
+++ b/Userland/arp.cpp
@@ -39,8 +39,9 @@ int main()
 
     printf("Address          HWaddress\n");
     auto file_contents = file->read_all();
-    auto json = JsonValue::from_string(file_contents).as_array();
-    json.for_each([](auto& value) {
+    auto json = JsonValue::from_string(file_contents);
+    ASSERT(json.has_value());
+    json.value().as_array().for_each([](auto& value) {
         auto if_object = value.as_object();
 
         auto ip_address = if_object.get("ip_address").to_string();
diff --git a/Userland/df.cpp b/Userland/df.cpp
index 9cf1def128855d..a8a65958679190 100644
--- a/Userland/df.cpp
+++ b/Userland/df.cpp
@@ -86,7 +86,9 @@ int main(int argc, char** argv)
     }
 
     auto file_contents = file->read_all();
-    auto json = JsonValue::from_string(file_contents).as_array();
+    auto json_result = JsonValue::from_string(file_contents);
+    ASSERT(json_result.has_value());
+    auto json = json_result.value().as_array();
     json.for_each([](auto& value) {
         auto fs_object = value.as_object();
         auto fs = fs_object.get("class_name").to_string();
diff --git a/Userland/gron.cpp b/Userland/gron.cpp
index 877327d417c9ed..f473fabbbc1f68 100644
--- a/Userland/gron.cpp
+++ b/Userland/gron.cpp
@@ -74,6 +74,7 @@ int main(int argc, char** argv)
 
     auto file_contents = file->read_all();
     auto json = JsonValue::from_string(file_contents);
+    ASSERT(json.has_value());
 
     if (use_color) {
         color_name = "\033[33;1m";
@@ -86,7 +87,7 @@ int main(int argc, char** argv)
     }
 
     Vector<String> trail;
-    print("json", json, trail);
+    print("json", json.value(), trail);
     return 0;
 }
 
@@ -116,7 +117,6 @@ static void print(const String& name, const JsonValue& value, Vector<String>& tr
     }
     switch (value.type()) {
     case JsonValue::Type::Null:
-    case JsonValue::Type::Undefined:
         printf("%s", color_null);
         break;
     case JsonValue::Type::Bool:
diff --git a/Userland/ifconfig.cpp b/Userland/ifconfig.cpp
index 65fc7f5a985896..9711fa8ccb21be 100644
--- a/Userland/ifconfig.cpp
+++ b/Userland/ifconfig.cpp
@@ -72,8 +72,9 @@ int main(int argc, char** argv)
         }
 
         auto file_contents = file->read_all();
-        auto json = JsonValue::from_string(file_contents).as_array();
-        json.for_each([](auto& value) {
+        auto json = JsonValue::from_string(file_contents);
+        ASSERT(json.has_value());
+        json.value().as_array().for_each([](auto& value) {
             auto if_object = value.as_object();
 
             auto name = if_object.get("name").to_string();
diff --git a/Userland/jp.cpp b/Userland/jp.cpp
index 75f8df2ab531a2..436eb97d2befa8 100644
--- a/Userland/jp.cpp
+++ b/Userland/jp.cpp
@@ -63,8 +63,9 @@ int main(int argc, char** argv)
 
     auto file_contents = file->read_all();
     auto json = JsonValue::from_string(file_contents);
+    ASSERT(json.has_value());
 
-    print(json);
+    print(json.value());
     printf("\n");
 
     return 0;
@@ -101,7 +102,7 @@ void print(const JsonValue& value, int indent)
         printf("\033[35;1m");
     else if (value.is_bool())
         printf("\033[32;1m");
-    else if (value.is_null() || value.is_undefined())
+    else if (value.is_null())
         printf("\033[34;1m");
     if (value.is_string())
         putchar('"');
diff --git a/Userland/lsirq.cpp b/Userland/lsirq.cpp
index 51a670c551a01b..5273142363e55a 100644
--- a/Userland/lsirq.cpp
+++ b/Userland/lsirq.cpp
@@ -60,8 +60,9 @@ int main(int argc, char** argv)
 
     printf("%4s  %-10s\n", " ", "CPU0");
     auto file_contents = proc_interrupts->read_all();
-    auto json = JsonValue::from_string(file_contents).as_array();
-    json.for_each([](auto& value) {
+    auto json = JsonValue::from_string(file_contents);
+    ASSERT(json.has_value());
+    json.value().as_array().for_each([](auto& value) {
         auto handler = value.as_object();
         auto purpose = handler.get("purpose").to_string();
         auto interrupt = handler.get("interrupt_line").to_string();
diff --git a/Userland/lspci.cpp b/Userland/lspci.cpp
index 8b80be2a548b5c..fefbf95085f3ed 100644
--- a/Userland/lspci.cpp
+++ b/Userland/lspci.cpp
@@ -69,8 +69,9 @@ int main(int argc, char** argv)
     }
 
     auto file_contents = proc_pci->read_all();
-    auto json = JsonValue::from_string(file_contents).as_array();
-    json.for_each([db](auto& value) {
+    auto json = JsonValue::from_string(file_contents);
+    ASSERT(json.has_value());
+    json.value().as_array().for_each([db](auto& value) {
         auto dev = value.as_object();
         auto seg = dev.get("seg").to_u32();
         auto bus = dev.get("bus").to_u32();
diff --git a/Userland/mount.cpp b/Userland/mount.cpp
index da75ea5e9ac763..697c37768679e6 100644
--- a/Userland/mount.cpp
+++ b/Userland/mount.cpp
@@ -149,9 +149,10 @@ bool print_mounts()
     }
 
     auto content = df->read_all();
-    auto json = JsonValue::from_string(content).as_array();
+    auto json = JsonValue::from_string(content);
+    ASSERT(json.has_value());
 
-    json.for_each([](auto& value) {
+    json.value().as_array().for_each([](auto& value) {
         auto fs_object = value.as_object();
         auto class_name = fs_object.get("class_name").to_string();
         auto mount_point = fs_object.get("mount_point").to_string();