diff --git a/src-ui/app/App.jsx b/src-ui/app/App.jsx
index 896cbb34..4374f7a9 100644
--- a/src-ui/app/App.jsx
+++ b/src-ui/app/App.jsx
@@ -1,13 +1,27 @@
-import { useEffect, useRef } from "react";
 import { useTranslation } from "react-i18next";
 
-import { useStartPython } from "@logics/useStartPython";
+import {
+    useWindow,
+} from "@logics_common";
+
+// import React from "react";
+
+import {
+    StartPythonController,
+    UiLanguageController,
+    ConfigPageCloseTriggerController,
+    UiSizeController,
+    FontFamilyController,
+    TransparencyController,
+} from "./_app_controllers/index.js";
+
 import { WindowTitleBar } from "./window_title_bar/WindowTitleBar";
 import { MainPage } from "./main_page/MainPage";
 import { ConfigPage } from "./config_page/ConfigPage";
 import { SplashComponent } from "./splash_component/SplashComponent";
 import { UpdatingComponent } from "./updating_component/UpdatingComponent";
 import { ModalController } from "./modal_controller/ModalController";
+import { SnackbarController } from "./snackbar_controller/SnackbarController";
 import styles from "./App.module.scss";
 import { useIsBackendReady, useIsSoftwareUpdating } from "@logics_common";
 
@@ -18,9 +32,9 @@ export const App = () => {
 
     return (
         <div className={styles.container}>
-            <StartPythonFacadeComponent />
+            <StartPythonController />
             <UiLanguageController />
-            <ConfigPageCloseTrigger />
+            <ConfigPageCloseTriggerController />
             <UiSizeController />
             <FontFamilyController />
             <TransparencyController />
@@ -45,160 +59,11 @@ const Contents = () => {
                 <ConfigPage />
                 <MainPage />
                 <ModalController />
+                <SnackbarController />
             </div>
             :
             <UpdatingComponent />
             }
         </>
     );
-};
-
-import {
-    useWindow,
-    useVolume,
-    useIsOpenedConfigPage,
-} from "@logics_common";
-
-import {
-    useUiLanguage,
-    useUiScaling,
-    useSelectedFontFamily,
-    useTransparency,
-} from "@logics_configs";
-
-import {
-    useMainFunction,
-} from "@logics_main";
-
-const StartPythonFacadeComponent = () => {
-    const { asyncStartPython } = useStartPython();
-    const hasRunRef = useRef(false);
-    const { asyncFetchFonts } = useAsyncFetchFonts();
-
-    useEffect(() => {
-        if (!hasRunRef.current) {
-            asyncStartPython().then(() => {
-                startFeedingToWatchDog();
-                asyncFetchFonts();
-            }).catch((err) => {
-                console.error(err);
-            });
-        }
-        return () => hasRunRef.current = true;
-    }, []);
-
-    return null;
-};
-
-const UiLanguageController = () => {
-    const { currentUiLanguage } = useUiLanguage();
-    const { i18n } = useTranslation();
-
-    useEffect(() => {
-        i18n.changeLanguage(currentUiLanguage.data);
-    }, [currentUiLanguage.data]);
-    return null;
-};
-
-import { useStore_MainFunctionsStateMemory } from "@store";
-
-const ConfigPageCloseTrigger = () => {
-    const { currentIsOpenedConfigPage } = useIsOpenedConfigPage();
-    const { currentMainFunctionsStateMemory, updateMainFunctionsStateMemory} = useStore_MainFunctionsStateMemory();
-    const {
-        currentTranscriptionSendStatus,
-        setTranscriptionSend,
-        currentTranscriptionReceiveStatus,
-        setTranscriptionReceive,
-    } = useMainFunction();
-    const {
-        currentMicThresholdCheckStatus,
-        volumeCheckStop_Mic,
-        currentSpeakerThresholdCheckStatus,
-        volumeCheckStop_Speaker,
-    } = useVolume();
-
-
-    const memorizeLatestMainFunctionsState = () => {
-        updateMainFunctionsStateMemory({
-            transcription_send: currentTranscriptionSendStatus.data,
-            transcription_receive: currentTranscriptionReceiveStatus.data,
-        });
-    };
-
-    const restoreMainFunctionState = () => {
-        if (currentMainFunctionsStateMemory.data.transcription_send === true) setTranscriptionSend(true);
-        if (currentMainFunctionsStateMemory.data.transcription_receive === true) setTranscriptionReceive(true);
-    };
-
-    useEffect(() => {
-        if (currentIsOpenedConfigPage.data === true) { // When config page is opened.
-            memorizeLatestMainFunctionsState();
-            if (currentTranscriptionSendStatus.data === true) setTranscriptionSend(false);
-            if (currentTranscriptionReceiveStatus.data === true) setTranscriptionReceive(false);
-        } else if (currentIsOpenedConfigPage.data === false) { // When config page is closed.
-            if (currentMicThresholdCheckStatus.data === true) volumeCheckStop_Mic();
-            if (currentSpeakerThresholdCheckStatus.data === true) volumeCheckStop_Speaker();
-            restoreMainFunctionState();
-        }
-    }, [currentIsOpenedConfigPage.data]);
-    return null;
-};
-
-import React from "react";
-const UiSizeController = () => {
-    const { currentUiScaling } = useUiScaling();
-    const font_size = 62.5 * currentUiScaling.data / 100;
-
-    useEffect(() => {
-        document.documentElement.style.setProperty("font-size", `${font_size}%`);
-    }, [currentUiScaling.data]);
-
-    return null;
-};
-
-
-const FontFamilyController = () => {
-    const { currentSelectedFontFamily } = useSelectedFontFamily();
-    useEffect(() => {
-        document.documentElement.style.setProperty("--font_family", currentSelectedFontFamily.data);
-    }, [currentSelectedFontFamily.data]);
-
-    return null;
-};
-
-import { useStore_SelectableFontFamilyList } from "@store";
-import { arrayToObject } from "@utils";
-
-import { invoke } from "@tauri-apps/api/tauri";
-const useAsyncFetchFonts = () => {
-    const { updateSelectableFontFamilyList } = useStore_SelectableFontFamilyList();
-    const asyncFetchFonts = async () => {
-        try {
-            let fonts = await invoke("get_font_list");
-            fonts = fonts.sort((a, b) => a.localeCompare(b, undefined, { sensitivity: "base" }));
-            updateSelectableFontFamilyList(arrayToObject(fonts));
-        } catch (error) {
-            console.error("Error fetching fonts:", error);
-        }
-    };
-    return { asyncFetchFonts };
-};
-
-
-const TransparencyController = () => {
-    const { currentTransparency } = useTransparency();
-    useEffect(() => {
-        document.documentElement.style.setProperty("opacity", `${currentTransparency.data / 100}`);
-    }, [currentTransparency.data]);
-
-    return null;
-};
-
-import { useStdoutToPython } from "@logics/useStdoutToPython";
-const startFeedingToWatchDog = () => {
-    const { asyncStdoutToPython } = useStdoutToPython();
-    setInterval(() => {
-        asyncStdoutToPython("/run/feed_watchdog");
-    }, 20000); // 20000ミリ秒 = 20秒
 };
\ No newline at end of file
diff --git a/src-ui/app/_app_controllers/ConfigPageCloseTriggerController.jsx b/src-ui/app/_app_controllers/ConfigPageCloseTriggerController.jsx
new file mode 100644
index 00000000..7705aecc
--- /dev/null
+++ b/src-ui/app/_app_controllers/ConfigPageCloseTriggerController.jsx
@@ -0,0 +1,55 @@
+import { useEffect } from "react";
+
+import {
+    useVolume,
+    useIsOpenedConfigPage,
+} from "@logics_common";
+
+import {
+    useMainFunction,
+} from "@logics_main";
+
+import { useStore_MainFunctionsStateMemory } from "@store";
+
+export const ConfigPageCloseTriggerController = () => {
+    const { currentIsOpenedConfigPage } = useIsOpenedConfigPage();
+    const { currentMainFunctionsStateMemory, updateMainFunctionsStateMemory} = useStore_MainFunctionsStateMemory();
+    const {
+        currentTranscriptionSendStatus,
+        setTranscriptionSend,
+        currentTranscriptionReceiveStatus,
+        setTranscriptionReceive,
+    } = useMainFunction();
+    const {
+        currentMicThresholdCheckStatus,
+        volumeCheckStop_Mic,
+        currentSpeakerThresholdCheckStatus,
+        volumeCheckStop_Speaker,
+    } = useVolume();
+
+
+    const memorizeLatestMainFunctionsState = () => {
+        updateMainFunctionsStateMemory({
+            transcription_send: currentTranscriptionSendStatus.data,
+            transcription_receive: currentTranscriptionReceiveStatus.data,
+        });
+    };
+
+    const restoreMainFunctionState = () => {
+        if (currentMainFunctionsStateMemory.data.transcription_send === true) setTranscriptionSend(true);
+        if (currentMainFunctionsStateMemory.data.transcription_receive === true) setTranscriptionReceive(true);
+    };
+
+    useEffect(() => {
+        if (currentIsOpenedConfigPage.data === true) { // When config page is opened.
+            memorizeLatestMainFunctionsState();
+            if (currentTranscriptionSendStatus.data === true) setTranscriptionSend(false);
+            if (currentTranscriptionReceiveStatus.data === true) setTranscriptionReceive(false);
+        } else if (currentIsOpenedConfigPage.data === false) { // When config page is closed.
+            if (currentMicThresholdCheckStatus.data === true) volumeCheckStop_Mic();
+            if (currentSpeakerThresholdCheckStatus.data === true) volumeCheckStop_Speaker();
+            restoreMainFunctionState();
+        }
+    }, [currentIsOpenedConfigPage.data]);
+    return null;
+};
\ No newline at end of file
diff --git a/src-ui/app/_app_controllers/FontFamilyController.jsx b/src-ui/app/_app_controllers/FontFamilyController.jsx
new file mode 100644
index 00000000..f7110d1d
--- /dev/null
+++ b/src-ui/app/_app_controllers/FontFamilyController.jsx
@@ -0,0 +1,11 @@
+import { useEffect } from "react";
+import { useSelectedFontFamily } from "@logics_configs";
+
+export const FontFamilyController = () => {
+    const { currentSelectedFontFamily } = useSelectedFontFamily();
+    useEffect(() => {
+        document.documentElement.style.setProperty("--font_family", currentSelectedFontFamily.data);
+    }, [currentSelectedFontFamily.data]);
+
+    return null;
+};
diff --git a/src-ui/app/_app_controllers/StartPythonController.jsx b/src-ui/app/_app_controllers/StartPythonController.jsx
new file mode 100644
index 00000000..62bf0b28
--- /dev/null
+++ b/src-ui/app/_app_controllers/StartPythonController.jsx
@@ -0,0 +1,48 @@
+import { invoke } from "@tauri-apps/api/tauri";
+import { useEffect, useRef } from "react";
+import { useStartPython } from "@logics/useStartPython";
+import { useStdoutToPython } from "@logics/useStdoutToPython";
+
+import { useStore_SelectableFontFamilyList } from "@store";
+import { arrayToObject } from "@utils";
+
+export const StartPythonController = () => {
+    const { asyncStartPython } = useStartPython();
+    const hasRunRef = useRef(false);
+    const { asyncFetchFonts } = useAsyncFetchFonts();
+
+    useEffect(() => {
+        if (!hasRunRef.current) {
+            asyncStartPython().then(() => {
+                startFeedingToWatchDogController();
+                asyncFetchFonts();
+            }).catch((err) => {
+                console.error(err);
+            });
+        }
+        return () => hasRunRef.current = true;
+    }, []);
+
+    return null;
+};
+
+const useAsyncFetchFonts = () => {
+    const { updateSelectableFontFamilyList } = useStore_SelectableFontFamilyList();
+    const asyncFetchFonts = async () => {
+        try {
+            let fonts = await invoke("get_font_list");
+            fonts = fonts.sort((a, b) => a.localeCompare(b, undefined, { sensitivity: "base" }));
+            updateSelectableFontFamilyList(arrayToObject(fonts));
+        } catch (error) {
+            console.error("Error fetching fonts:", error);
+        }
+    };
+    return { asyncFetchFonts };
+};
+
+const startFeedingToWatchDogController = () => {
+    const { asyncStdoutToPython } = useStdoutToPython();
+    setInterval(() => {
+        asyncStdoutToPython("/run/feed_watchdog");
+    }, 20000); // 20000ミリ秒 = 20秒
+};
\ No newline at end of file
diff --git a/src-ui/app/_app_controllers/TransparencyController.jsx b/src-ui/app/_app_controllers/TransparencyController.jsx
new file mode 100644
index 00000000..46982413
--- /dev/null
+++ b/src-ui/app/_app_controllers/TransparencyController.jsx
@@ -0,0 +1,11 @@
+import { useEffect } from "react";
+import { useTransparency } from "@logics_configs";
+
+export const TransparencyController = () => {
+    const { currentTransparency } = useTransparency();
+    useEffect(() => {
+        document.documentElement.style.setProperty("opacity", `${currentTransparency.data / 100}`);
+    }, [currentTransparency.data]);
+
+    return null;
+};
\ No newline at end of file
diff --git a/src-ui/app/_app_controllers/UiLanguageController.jsx b/src-ui/app/_app_controllers/UiLanguageController.jsx
new file mode 100644
index 00000000..5b45c503
--- /dev/null
+++ b/src-ui/app/_app_controllers/UiLanguageController.jsx
@@ -0,0 +1,14 @@
+import { useEffect } from "react";
+
+import { useTranslation } from "react-i18next";
+import { useUiLanguage } from "@logics_configs";
+
+export const UiLanguageController = () => {
+    const { currentUiLanguage } = useUiLanguage();
+    const { i18n } = useTranslation();
+
+    useEffect(() => {
+        i18n.changeLanguage(currentUiLanguage.data);
+    }, [currentUiLanguage.data]);
+    return null;
+};
\ No newline at end of file
diff --git a/src-ui/app/_app_controllers/UiSizeController.jsx b/src-ui/app/_app_controllers/UiSizeController.jsx
new file mode 100644
index 00000000..8b970c0f
--- /dev/null
+++ b/src-ui/app/_app_controllers/UiSizeController.jsx
@@ -0,0 +1,13 @@
+import { useEffect } from "react";
+import { useUiScaling } from "@logics_configs";
+
+export const UiSizeController = () => {
+    const { currentUiScaling } = useUiScaling();
+    const font_size = 62.5 * currentUiScaling.data / 100;
+
+    useEffect(() => {
+        document.documentElement.style.setProperty("font-size", `${font_size}%`);
+    }, [currentUiScaling.data]);
+
+    return null;
+};
\ No newline at end of file
diff --git a/src-ui/app/_app_controllers/index.js b/src-ui/app/_app_controllers/index.js
new file mode 100644
index 00000000..f91d40ac
--- /dev/null
+++ b/src-ui/app/_app_controllers/index.js
@@ -0,0 +1,6 @@
+export { StartPythonController } from "./StartPythonController";
+export { UiLanguageController } from "./UiLanguageController";
+export { ConfigPageCloseTriggerController } from "./ConfigPageCloseTriggerController";
+export { UiSizeController } from "./UiSizeController";
+export { FontFamilyController } from "./FontFamilyController";
+export { TransparencyController } from "./TransparencyController";
\ No newline at end of file
diff --git a/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.jsx b/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.jsx
index dc6f4309..e8bba371 100644
--- a/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.jsx
+++ b/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.jsx
@@ -1,3 +1,4 @@
+import clsx from "clsx";
 import React, { useRef, forwardRef, useImperativeHandle } from "react";
 import styles from "./_Entry.module.scss";
 
@@ -9,6 +10,9 @@ const _Entry = forwardRef((props, ref) => {
             inputRef.current.focus();
         }
     }));
+    const input_class_names = clsx(styles.entry_input_area, {
+        [styles.is_disabled]: props.is_disabled
+    });
 
     return (
         <div className={styles.entry_container}>
@@ -18,7 +22,7 @@ const _Entry = forwardRef((props, ref) => {
             >
                 <input
                     ref={inputRef}
-                    className={styles.entry_input_area}
+                    className={input_class_names}
                     value={props.ui_variable === null ? "" : props.ui_variable}
                     onChange={(e) => props.onChange(e)}
                 />
diff --git a/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.module.scss b/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.module.scss
index dc2ac749..c9744de6 100644
--- a/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.module.scss
+++ b/src-ui/app/config_page/setting_section/setting_box/_components/_atoms/_entry/_Entry.module.scss
@@ -16,4 +16,9 @@
     height: 100%;
     font-size: 1.4rem;
     resize: none;
+    color: var(--dark_basic_text_color);
+    &.is_disabled {
+        color: var(--dark_500_color);
+        pointer-events: none;
+    }
 }
\ No newline at end of file
diff --git a/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.jsx b/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.jsx
index 0a1dea91..42401b7a 100644
--- a/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.jsx
+++ b/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.jsx
@@ -1,9 +1,11 @@
 import styles from "./DeeplAuthKey.module.scss";
 import { useTranslation } from "react-i18next";
 import clsx from "clsx";
+import CircularProgress from "@mui/material/CircularProgress";
 import ExternalLink from "@images/external_link.svg?react";
 import { _Entry } from "../_atoms/_entry/_Entry";
 import { useState, useRef } from "react";
+import { useEffect } from "react";
 
 export const DeeplAuthKey = (props) => {
     const { t } = useTranslation();
@@ -22,11 +24,28 @@ export const DeeplAuthKey = (props) => {
         props.saveFunction();
     };
 
+    useEffect(() => {
+        if (props.variable === "" || props.variable === null) {
+            seIsEditable(true);
+        }
+    }, [props.variable]);
+
+    const is_disabled = props.state === "pending";
+
+    const save_button_class_names = clsx(styles.save_button, {
+        [styles.is_disabled]: is_disabled
+    });
+
     return (
         <div className={styles.container}>
             <div className={styles.entry_section_wrapper}>
-                <_Entry ref={entryRef} width="30rem" onChange={onchangeEntryAuthKey} ui_variable={props.variable}/>
-                <button className={styles.save_button} onClick={saveAuthKey}>Save</button>
+                <_Entry ref={entryRef} width="30rem" onChange={onchangeEntryAuthKey} ui_variable={props.variable} is_disabled={is_disabled}/>
+                <button className={save_button_class_names} onClick={saveAuthKey}>
+                    {is_disabled
+                    ? <CircularProgress size="1.4rem" sx={{ color: "var(--dark_basic_text_color)" }}/>
+                    : <p className={styles.save_button_label}>Save</p>
+                }
+                </button>
                 {is_editable
                 ? null
                 :
diff --git a/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.module.scss b/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.module.scss
index 6e5a3411..575ec8bc 100644
--- a/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.module.scss
+++ b/src-ui/app/config_page/setting_section/setting_box/_components/deepl_auth_key/DeeplAuthKey.module.scss
@@ -44,17 +44,25 @@
 .save_button {
     padding: 0.8rem 1.2rem;
     background-color: var(--primary_600_color);
-    color: var(--dark_basic_text_color);
-    font-size: 1.4rem;
     border-radius: 0.4rem;
     text-align: center;
     flex-shrink: 0;
+    min-width: 5.4rem;
     &:hover {
         background-color: var(--primary_500_color);
     }
     &:active {
         background-color: var(--primary_700_color);
     }
+    &.is_disabled {
+        pointer-events: none;
+        background-color: var(--primary_800_color);
+    }
+}
+
+.save_button_label {
+    color: var(--dark_basic_text_color);
+    font-size: 1.4rem;
 }
 
 .open_webpage_button_wrapper {
diff --git a/src-ui/app/config_page/setting_section/setting_box/_components/threshold_component/threshold_entry/ThresholdEntry.module.scss b/src-ui/app/config_page/setting_section/setting_box/_components/threshold_component/threshold_entry/ThresholdEntry.module.scss
index d2378d03..929f8975 100644
--- a/src-ui/app/config_page/setting_section/setting_box/_components/threshold_component/threshold_entry/ThresholdEntry.module.scss
+++ b/src-ui/app/config_page/setting_section/setting_box/_components/threshold_component/threshold_entry/ThresholdEntry.module.scss
@@ -1,4 +1,5 @@
 .container {
+
 }
 
 .entry_wrapper {
diff --git a/src-ui/app/config_page/setting_section/setting_box/translation/Translation.jsx b/src-ui/app/config_page/setting_section/setting_box/translation/Translation.jsx
index e0f02565..95ebdb54 100644
--- a/src-ui/app/config_page/setting_section/setting_box/translation/Translation.jsx
+++ b/src-ui/app/config_page/setting_section/setting_box/translation/Translation.jsx
@@ -98,9 +98,9 @@ const CTranslation2ComputeDevice_Box = () => {
 };
 
 const DeeplAuthKey_Box = () => {
-    const [input_value, seInputValue] = useState("");
     const { t } = useTranslation();
     const { currentDeepLAuthKey, setDeepLAuthKey, deleteDeepLAuthKey } = useDeepLAuthKey();
+    const [input_value, seInputValue] = useState(currentDeepLAuthKey.data);
 
     const onChangeFunction = (value) => {
         seInputValue(value);
@@ -124,6 +124,7 @@ const DeeplAuthKey_Box = () => {
                     {translator: t("main_page.translator")}
                 )}
                 variable={input_value}
+                state={currentDeepLAuthKey.state}
                 onChangeFunction={onChangeFunction}
                 saveFunction={saveFunction}
             />
@@ -169,4 +170,4 @@ const findKeyByDeviceValue = (devices, target_value) => {
         }
     }
     return null;
-};
+};
\ No newline at end of file
diff --git a/src-ui/app/main_page/main_section/message_container/MessageContainer.jsx b/src-ui/app/main_page/main_section/message_container/MessageContainer.jsx
index cad18079..dbc5c100 100644
--- a/src-ui/app/main_page/main_section/message_container/MessageContainer.jsx
+++ b/src-ui/app/main_page/main_section/message_container/MessageContainer.jsx
@@ -14,7 +14,7 @@ export const MessageContainer = () => {
     const { currentUiScaling } = useUiScaling();
     const [is_hovered, setIsHovered] = useState(false);
     const [message_box_height_in_rem, setMessageBoxHeightInRem] = useState(10);
-    const FONT_SIZE_STANDARD = 10 * currentUiScaling.data / 100;  // 10px = 1rem
+    const FONT_SIZE_STANDARD = 10 * currentUiScaling.data / 100; // 10px = 1rem
     const { currentIsAppliedInitMessageBoxHeight, updateIsAppliedInitMessageBoxHeight } = useStore_IsAppliedInitMessageBoxHeight();
 
     const container_ref = useRef(null);
@@ -23,9 +23,10 @@ export const MessageContainer = () => {
 
     const asyncSetMessageBoxHeightInRem = async (data) => {
         const minimized = await appWindow.isMinimized();
-        if (minimized === true) return; // don't save while the window is minimized.
+        if (minimized) return; // don't save while the window is minimized.
         setMessageBoxHeightInRem(data);
     };
+
     const calculateMessageBoxRatioAndHeight = () => {
         if (!currentIsAppliedInitMessageBoxHeight.data) {
             asyncSetMessageInputBoxRatio(currentMessageInputBoxRatio.data);
@@ -33,7 +34,7 @@ export const MessageContainer = () => {
             return;
         }
 
-        if (log_box_ref.current && message_box_wrapper_ref.current) {
+        if (log_box_ref.current && message_box_wrapper_ref.current && container_ref.current) {
             const container_height = container_ref.current.offsetHeight;
             const container_padding_bottom = parseFloat(window.getComputedStyle(container_ref.current).paddingBottom);
             const total_height = container_height - container_padding_bottom;
@@ -43,6 +44,8 @@ export const MessageContainer = () => {
 
             asyncSetMessageInputBoxRatio(message_box_ratio);
             asyncSetMessageBoxHeightInRem(convertRatioToRem(message_box_ratio));
+        } else {
+            console.warn("References not ready for calculation");
         }
     };
 
@@ -53,24 +56,26 @@ export const MessageContainer = () => {
     });
 
     useEffect(() => {
-        // Note: I thought the part "1.4" is message box bottom padding + (message box separator height/2)
-        // but it should be fixed at 1.4. Idk why, tho.
         asyncSetMessageBoxHeightInRem((position / FONT_SIZE_STANDARD) - 1.4);
     }, [position]);
 
-
     useEffect(() => {
         asyncSetMessageBoxHeightInRem(convertRatioToRem(currentMessageInputBoxRatio.data));
     }, [currentMessageInputBoxRatio.data]);
 
     const convertRatioToRem = (ratio) => {
+        if (!container_ref.current) return 0;
         const container_height = container_ref.current.offsetHeight;
         const container_padding_bottom = parseFloat(window.getComputedStyle(container_ref.current).paddingBottom);
         const total_height = container_height - container_padding_bottom;
-        if (total_height === 0) return 0;
-        return ((ratio / 100) * total_height / FONT_SIZE_STANDARD);
+        return total_height === 0 ? 0 : ((ratio / 100) * total_height / FONT_SIZE_STANDARD);
     };
 
+    useEffect(() => {
+        calculateMessageBoxRatioAndHeight();
+        updateIsAppliedInitMessageBoxHeight(true); // Ensure this happens after initial calculation
+    }, []);
+
     useEffect(() => {
         let resizeTimeout;
 
@@ -86,10 +91,6 @@ export const MessageContainer = () => {
         };
     }, []);
 
-    useEffect(() => {
-        updateIsAppliedInitMessageBoxHeight(true);
-    }, []);
-
     return (
         <div className={styles.container} ref={container_ref}>
             <div className={styles.log_box_resize_wrapper}
@@ -98,7 +99,7 @@ export const MessageContainer = () => {
                 onMouseLeave={() => setIsHovered(false)}
             >
                 <LogBox />
-                <MessageLogSettingsContainer to_visible_toggle_bar={is_hovered}/>
+                <MessageLogSettingsContainer to_visible_toggle_bar={is_hovered} />
             </div>
             <Separator {...separatorProps} onDragStart={calculateMessageBoxRatioAndHeight} />
             <div
@@ -112,10 +113,8 @@ export const MessageContainer = () => {
     );
 };
 
-const Separator = ({ onDragStart, ...props }) => {
-    return (
-        <div tabIndex={0} className={styles.separator} {...props} onDragStart={onDragStart}>
-            <span className={styles.separator_line}></span>
-        </div>
-    );
-};
+const Separator = ({ onDragStart, ...props }) => (
+    <div tabIndex={0} className={styles.separator} {...props} onDragStart={onDragStart}>
+        <span className={styles.separator_line}></span>
+    </div>
+);
diff --git a/src-ui/app/snackbar_controller/SnackbarController.jsx b/src-ui/app/snackbar_controller/SnackbarController.jsx
new file mode 100644
index 00000000..dcc8f54a
--- /dev/null
+++ b/src-ui/app/snackbar_controller/SnackbarController.jsx
@@ -0,0 +1,39 @@
+import { clsx } from "clsx";
+import Snackbar from "@mui/material/Snackbar";
+import Slide from "@mui/material/Slide";
+
+import styles from "./SnackbarController.module.scss";
+import { useNotificationStatus } from "@logics_common";
+
+export const SnackbarController = () => {
+    const { currentNotificationStatus, closeNotification } = useNotificationStatus();
+
+    const handleClose = (event, reason) => {
+        closeNotification(event, reason);
+    };
+
+    const snackbar_classname = clsx(styles.snackbar_content, {
+        [styles.is_success]: currentNotificationStatus.data.status === "success",
+        [styles.is_error]: currentNotificationStatus.data.status === "error",
+    });
+
+    return (
+        <div>
+            <Snackbar
+                open={currentNotificationStatus.data.is_open}
+                onClose={handleClose}
+                TransitionComponent={SlideTransition}
+                key={currentNotificationStatus.data.key}
+                autoHideDuration={5000}
+            >
+                <div className={snackbar_classname}>
+                    <p className={styles.snackbar_message}>{currentNotificationStatus.data.message}</p>
+                </div>
+            </Snackbar>
+        </div>
+    );
+};
+
+const SlideTransition = (props) => {
+    return <Slide {...props} direction="up" />;
+};
diff --git a/src-ui/app/snackbar_controller/SnackbarController.module.scss b/src-ui/app/snackbar_controller/SnackbarController.module.scss
new file mode 100644
index 00000000..2db44fa9
--- /dev/null
+++ b/src-ui/app/snackbar_controller/SnackbarController.module.scss
@@ -0,0 +1,16 @@
+.snackbar_content {
+    width: 100%;
+    height: 100%;
+    padding: 2rem;
+    color: #fff;
+    &.is_success {
+        background-color: #368777;
+    }
+    &.is_error {
+        background-color: #bb4448;
+    }
+}
+
+.snackbar_message {
+    font-size: 1.4rem;
+}
\ No newline at end of file
diff --git a/src-ui/logics/common/index.js b/src-ui/logics/common/index.js
index 8f1cd737..e63b28db 100644
--- a/src-ui/logics/common/index.js
+++ b/src-ui/logics/common/index.js
@@ -5,6 +5,7 @@ export { useWindow } from "./useWindow";
 export { useIsOpenedConfigPage } from "./useIsOpenedConfigPage";
 export { useIsSoftwareUpdateAvailable } from "./useIsSoftwareUpdateAvailable";
 export { useIsSoftwareUpdating } from "./useIsSoftwareUpdating";
+export { useNotificationStatus } from "./useNotificationStatus";
 export { useOpenFolder } from "./useOpenFolder";
 export { useMessage } from "./useMessage";
 export { useUpdateSoftware } from "./useUpdateSoftware";
diff --git a/src-ui/logics/common/useNotificationStatus.js b/src-ui/logics/common/useNotificationStatus.js
new file mode 100644
index 00000000..f36c0c45
--- /dev/null
+++ b/src-ui/logics/common/useNotificationStatus.js
@@ -0,0 +1,42 @@
+import { useStore_NotificationStatus } from "@store";
+
+export const useNotificationStatus = () => {
+    const { currentNotificationStatus, updateNotificationStatus } = useStore_NotificationStatus();
+
+    const generateRandomKey = () => Math.random();
+
+    const showNotification_Error = (message) => {
+        updateNotificationStatus({
+            status: "error",
+            is_open: true,
+            key: generateRandomKey(),
+            message: message,
+        });
+    };
+
+    const showNotification_Success = (message) => {
+        updateNotificationStatus({
+            status: "success",
+            is_open: true,
+            key: generateRandomKey(),
+            message: message,
+        });
+    };
+
+    const closeNotification = (event, reason) => {
+        if (reason === "clickaway") return;
+        updateNotificationStatus((prev) => ({
+            ...prev.data,
+            is_open: false,
+        }));
+    };
+
+    return {
+        currentNotificationStatus,
+        updateNotificationStatus,
+
+        showNotification_Error,
+        showNotification_Success,
+        closeNotification,
+    };
+};
\ No newline at end of file
diff --git a/src-ui/logics/useReceiveRoutes.js b/src-ui/logics/useReceiveRoutes.js
index 748b5061..0c09da4f 100644
--- a/src-ui/logics/useReceiveRoutes.js
+++ b/src-ui/logics/useReceiveRoutes.js
@@ -2,6 +2,9 @@ import { translator_status } from "@ui_configs";
 import { arrayToObject } from "@utils";
 
 import {
+    useNotificationStatus,
+
+
     useComputeMode,
     useInitProgress,
     useIsBackendReady,
@@ -167,6 +170,10 @@ export const useReceiveRoutes = () => {
     const { updateOscIpAddress } = useOscIpAddress();
     const { updateOscPort } = useOscPort();
 
+
+
+    const { showNotification_Success, showNotification_Error } = useNotificationStatus();
+
     const routes = {
         // Common
         "/run/feed_watchdog": () => {},
@@ -494,6 +501,7 @@ export const useReceiveRoutes = () => {
                 const error_route = error_routes[parsed_data.endpoint];
                 (error_route) ? error_route(parsed_data.result.data) : console.error(`Invalid endpoint: ${parsed_data.endpoint}\nresult: ${JSON.stringify(parsed_data.result)}`);
                 console.error(`status 400: ${JSON.stringify(parsed_data.result)}`);
+                showNotification_Error(parsed_data.result.message);
                 break;
 
             case 348:
diff --git a/src-ui/store.js b/src-ui/store.js
index cf63e236..878911cc 100644
--- a/src-ui/store.js
+++ b/src-ui/store.js
@@ -115,6 +115,12 @@ export const { atomInstance: Atom_IsSoftwareUpdateAvailable, useHook: useStore_I
 export const { atomInstance: Atom_InitProgress, useHook: useStore_InitProgress } = createAtomWithHook(0, "InitProgress");
 export const { atomInstance: Atom_IsBreakPoint, useHook: useStore_IsBreakPoint } = createAtomWithHook(false, "IsBreakPoint");
 export const { atomInstance: Atom_IsSoftwareUpdating, useHook: useStore_IsSoftwareUpdating } = createAtomWithHook(false, "IsSoftwareUpdating");
+export const { atomInstance: Atom_NotificationStatus, useHook: useStore_NotificationStatus } = createAtomWithHook({
+    status: "",
+    is_open: false,
+    key: 0,
+    message: "",
+}, "NotificationStatus");
 
 // Main Page
 // Functions