diff --git a/Editor/UpdateNotification.meta b/Editor/UpdateNotification.meta
new file mode 100644
index 0000000..d6b105b
--- /dev/null
+++ b/Editor/UpdateNotification.meta
@@ -0,0 +1,8 @@
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diff --git a/Editor/UpdateNotification/ReleaseChecker.cs b/Editor/UpdateNotification/ReleaseChecker.cs
new file mode 100644
index 0000000..21532cc
--- /dev/null
+++ b/Editor/UpdateNotification/ReleaseChecker.cs
@@ -0,0 +1,197 @@
+using System;
+using System.Collections;
+using System.Security.Cryptography;
+using System.Text;
+using UnityEditor;
+using UnityEngine;
+
+namespace Net._32ba.GitTool.UpdateNotification
+{
+    [InitializeOnLoad]
+    internal static class ReleaseChecker
+    {
+        private const string PackageId = "net.32ba.git-tool";
+        private const string PackageDisplayName = "Git Tool";
+        private const string ReleasePageUrl = "https://github.com/32ba/VRC-git-tool/releases";
+        private const string LastCheckKeyPrefix = "net.32ba.git.tool.LastVersionCheck";
+        private const double CheckIntervalHours = 24.0;
+
+        private static readonly VpmApiClient Api = new VpmApiClient(PackageId);
+
+        private static string LatestVersion { get; set; }
+        private static bool HasNewVersion { get; set; }
+        private static bool IsChecking { get; set; }
+        private static string CheckError { get; set; }
+
+        static ReleaseChecker()
+        {
+            EditorApplication.delayCall += () => CheckForUpdates(false);
+        }
+
+        private static void CheckForUpdates(bool forceCheck)
+        {
+            if (IsChecking)
+                return;
+
+            if (!forceCheck && !ShouldCheckForUpdates())
+                return;
+
+            IsChecking = true;
+            HasNewVersion = false;
+            CheckError = null;
+
+            EditorCoroutine.Start(CheckRoutine(forceCheck));
+        }
+
+        private static string GetCurrentVersion()
+        {
+            try
+            {
+                var packageInfo = UnityEditor.PackageManager.PackageInfo.FindForAssembly(typeof(ReleaseChecker).Assembly);
+                if (packageInfo != null && !string.IsNullOrEmpty(packageInfo.version))
+                    return packageInfo.version;
+            }
+            catch (Exception ex)
+            {
+                Debug.LogWarning($"[{PackageDisplayName}] Failed to read package version: {ex.Message}");
+            }
+
+            return "0.0.0";
+        }
+
+        private static IEnumerator CheckRoutine(bool forceCheck)
+        {
+            yield return Api.GetLatestVersionCoroutine(
+                latest => HandleSuccess(latest, forceCheck),
+                error => HandleError(error, forceCheck));
+        }
+
+        private static void HandleSuccess(string latest, bool forceCheck)
+        {
+            IsChecking = false;
+
+            if (string.IsNullOrEmpty(latest))
+            {
+                CheckError = "Empty version response";
+                if (forceCheck)
+                    EditorUtility.DisplayDialog($"{PackageDisplayName} Update Check", CheckError, "OK");
+                return;
+            }
+
+            LatestVersion = latest;
+            var current = GetCurrentVersion();
+            EditorPrefs.SetString(GetLastCheckKey(), DateTime.Now.ToBinary().ToString());
+
+            if (VersionUtility.IsNewerVersion(current, latest))
+            {
+                HasNewVersion = true;
+                Debug.Log($"[{PackageDisplayName}] New version available: {current} -> {latest}");
+                ShowUpdateDialog(current, latest);
+            }
+            else if (forceCheck)
+            {
+                EditorUtility.DisplayDialog(
+                    $"{PackageDisplayName} Update Check",
+                    $"{PackageDisplayName} is up to date.\n\nCurrent: {VersionUtility.FormatVersion(current)}",
+                    "OK");
+            }
+            else
+            {
+                Debug.Log($"[{PackageDisplayName}] Package is up to date: {current}");
+            }
+        }
+
+        private static void HandleError(string error, bool forceCheck)
+        {
+            IsChecking = false;
+            CheckError = error;
+            Debug.LogWarning($"[{PackageDisplayName}] Update check failed: {error}");
+
+            if (forceCheck)
+                EditorUtility.DisplayDialog($"{PackageDisplayName} Update Check", $"Update check failed.\n\n{error}", "OK");
+        }
+
+        private static void ShowUpdateDialog(string current, string latest)
+        {
+            if (EditorUtility.DisplayDialog(
+                    $"{PackageDisplayName} Update Available",
+                    $"A new version of {PackageDisplayName} is available.\n\n{VersionUtility.FormatVersion(current)} -> {VersionUtility.FormatVersion(latest)}",
+                    "Open Release Page",
+                    "Later"))
+            {
+                Application.OpenURL(ReleasePageUrl);
+            }
+        }
+
+        private static bool ShouldCheckForUpdates()
+        {
+            var stored = EditorPrefs.GetString(GetLastCheckKey(), "");
+            if (string.IsNullOrEmpty(stored))
+                return true;
+
+            if (long.TryParse(stored, out var binary))
+            {
+                var last = DateTime.FromBinary(binary);
+                return (DateTime.Now - last).TotalHours >= CheckIntervalHours;
+            }
+
+            return true;
+        }
+
+        private static string GetLastCheckKey()
+        {
+            return $"{LastCheckKeyPrefix}.{GetProjectScopeSuffix()}";
+        }
+
+        private static string GetProjectScopeSuffix()
+        {
+            var projectPath = Application.dataPath;
+            if (string.IsNullOrEmpty(projectPath))
+                return "unknown";
+
+            using (var sha1 = SHA1.Create())
+            {
+                var bytes = Encoding.UTF8.GetBytes(projectPath);
+                var hash = sha1.ComputeHash(bytes);
+                return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
+            }
+        }
+    }
+
+    internal sealed class EditorCoroutine
+    {
+        private readonly IEnumerator _routine;
+        private IEnumerator _nested;
+
+        public static EditorCoroutine Start(IEnumerator routine)
+        {
+            var coroutine = new EditorCoroutine(routine);
+            EditorApplication.update += coroutine.Update;
+            return coroutine;
+        }
+
+        private EditorCoroutine(IEnumerator routine)
+        {
+            _routine = routine;
+        }
+
+        private void Update()
+        {
+            if (_nested != null)
+            {
+                if (_nested.MoveNext())
+                    return;
+                _nested = null;
+            }
+
+            if (!_routine.MoveNext())
+            {
+                EditorApplication.update -= Update;
+                return;
+            }
+
+            if (_routine.Current is IEnumerator nestedRoutine)
+                _nested = nestedRoutine;
+        }
+    }
+}
diff --git a/Editor/UpdateNotification/ReleaseChecker.cs.meta b/Editor/UpdateNotification/ReleaseChecker.cs.meta
new file mode 100644
index 0000000..217f4a9
--- /dev/null
+++ b/Editor/UpdateNotification/ReleaseChecker.cs.meta
@@ -0,0 +1,11 @@
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diff --git a/Editor/UpdateNotification/VersionUtility.cs b/Editor/UpdateNotification/VersionUtility.cs
new file mode 100644
index 0000000..c91b8fb
--- /dev/null
+++ b/Editor/UpdateNotification/VersionUtility.cs
@@ -0,0 +1,58 @@
+using System;
+using System.Text.RegularExpressions;
+using UnityEngine;
+
+namespace Net._32ba.GitTool.UpdateNotification
+{
+    internal static class VersionUtility
+    {
+        public static bool IsNewerVersion(string currentVersion, string latestVersion)
+        {
+            if (string.IsNullOrEmpty(currentVersion) || string.IsNullOrEmpty(latestVersion))
+                return false;
+
+            try
+            {
+                return ParseVersion(latestVersion) > ParseVersion(currentVersion);
+            }
+            catch (Exception ex)
+            {
+                Debug.LogWarning($"[Git Tool] Failed to compare versions '{currentVersion}' and '{latestVersion}': {ex.Message}");
+                return false;
+            }
+        }
+
+        public static string FormatVersion(string version)
+        {
+            if (string.IsNullOrEmpty(version))
+                return "Unknown";
+
+            return version.StartsWith("v", StringComparison.OrdinalIgnoreCase) ? version : "v" + version;
+        }
+
+        private static Version ParseVersion(string versionString)
+        {
+            var clean = versionString.TrimStart('v', 'V');
+
+            var match = Regex.Match(clean, @"^(\d+)\.(\d+)\.(\d+)");
+            if (match.Success)
+            {
+                return new Version(
+                    int.Parse(match.Groups[1].Value),
+                    int.Parse(match.Groups[2].Value),
+                    int.Parse(match.Groups[3].Value));
+            }
+
+            match = Regex.Match(clean, @"^(\d+)\.(\d+)");
+            if (match.Success)
+            {
+                return new Version(
+                    int.Parse(match.Groups[1].Value),
+                    int.Parse(match.Groups[2].Value),
+                    0);
+            }
+
+            return new Version(clean);
+        }
+    }
+}
diff --git a/Editor/UpdateNotification/VersionUtility.cs.meta b/Editor/UpdateNotification/VersionUtility.cs.meta
new file mode 100644
index 0000000..a468201
--- /dev/null
+++ b/Editor/UpdateNotification/VersionUtility.cs.meta
@@ -0,0 +1,11 @@
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diff --git a/Editor/UpdateNotification/VpmApiClient.cs b/Editor/UpdateNotification/VpmApiClient.cs
new file mode 100644
index 0000000..f221baf
--- /dev/null
+++ b/Editor/UpdateNotification/VpmApiClient.cs
@@ -0,0 +1,63 @@
+using System;
+using System.Collections;
+using System.Text;
+using UnityEngine;
+using UnityEngine.Networking;
+
+namespace Net._32ba.GitTool.UpdateNotification
+{
+    internal sealed class VpmApiClient
+    {
+        private const string ApiBaseUrl = "https://vpm.32ba.net/api/packages";
+        private const int RequestTimeoutSeconds = 10;
+        private readonly string _packageId;
+
+        public VpmApiClient(string packageId)
+        {
+            _packageId = packageId;
+        }
+
+        public IEnumerator GetLatestVersionCoroutine(Action<string> onComplete, Action<string> onError = null)
+        {
+            var url = $"{ApiBaseUrl}/{_packageId}/latest/version";
+
+            using (var request = UnityWebRequest.Get(url))
+            {
+                request.timeout = RequestTimeoutSeconds;
+                request.SetRequestHeader("User-Agent", $"32ba-UnityUpdateChecker/{Application.unityVersion}");
+                yield return request.SendWebRequest();
+
+                if (request.result == UnityWebRequest.Result.Success)
+                    onComplete?.Invoke(request.downloadHandler.text.Trim());
+                else
+                    onError?.Invoke(BuildErrorMessage(request, url));
+            }
+        }
+
+        private static string BuildErrorMessage(UnityWebRequest request, string url)
+        {
+            var parts = new StringBuilder();
+            parts.Append("VPM API request failed");
+            parts.Append($" ({request.result})");
+
+            if (!string.IsNullOrEmpty(request.error))
+                parts.Append($": {request.error}");
+
+            if (request.responseCode > 0)
+                parts.Append($" [HTTP {request.responseCode}]");
+
+            parts.Append($" URL={url}");
+
+            var responseText = request.downloadHandler != null ? request.downloadHandler.text : null;
+            if (!string.IsNullOrWhiteSpace(responseText))
+            {
+                responseText = responseText.Trim();
+                if (responseText.Length > 200)
+                    responseText = responseText.Substring(0, 200) + "...";
+                parts.Append($" Response={responseText}");
+            }
+
+            return parts.ToString();
+        }
+    }
+}
diff --git a/Editor/UpdateNotification/VpmApiClient.cs.meta b/Editor/UpdateNotification/VpmApiClient.cs.meta
new file mode 100644
index 0000000..0e15d13
--- /dev/null
+++ b/Editor/UpdateNotification/VpmApiClient.cs.meta
@@ -0,0 +1,11 @@
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